Taint issue

[Smacker]

Some users (but not myself) are seeing a taint error with my addon (PowerAuras) when they open the world map and are in combat. Log looks like this:

12/16 09:07:56.195  Global variable uncheckImage tainted by PowerAuras - Interface\FrameXML\UIDropDownMenu.lua:500 UIDropDownMenu_Refresh()
12/16 09:07:56.195      Interface\FrameXML\UIDropDownMenu.lua:568 UIDropDownMenu_SetSelectedID()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:661 WorldMapZoneDropDown_Update()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:1686 WorldMapFrame_UpdateMap()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:190
12/16 09:07:56.195      SetMapToCurrentZone()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:157
12/16 09:07:56.195      WorldMapFrame:Show()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1420 <unnamed>:SetUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1262 <unnamed>:ShowUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1198
12/16 09:07:56.195      <unnamed>:SetAttribute()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1878 ShowUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1862 ToggleFrame()
12/16 09:07:56.195      TOGGLEWORLDMAP:1
12/16 09:07:56.195  Execution tainted by PowerAuras while reading uncheckImage - Interface\FrameXML\UIDropDownMenu.lua:938 UIDropDownMenu_ClearAll()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:684 WorldMapLevelDropDown_Update()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:1687 WorldMapFrame_UpdateMap()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:190
12/16 09:07:56.195      SetMapToCurrentZone()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:157
12/16 09:07:56.195      WorldMapFrame:Show()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1420 <unnamed>:SetUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1262 <unnamed>:ShowUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1198
12/16 09:07:56.195      <unnamed>:SetAttribute()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1878 ShowUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1862 ToggleFrame()
12/16 09:07:56.195      TOGGLEWORLDMAP:1
12/16 09:07:56.195  An action was blocked in combat because of taint from PowerAuras - WorldMapBlobFrame:Hide()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:1634 WorldMapFrame_DisplayQuests()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:1690 WorldMapFrame_UpdateMap()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:190
12/16 09:07:56.195      SetMapToCurrentZone()
12/16 09:07:56.195      Interface\FrameXML\WorldMapFrame.lua:157
12/16 09:07:56.195      WorldMapFrame:Show()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1420 <unnamed>:SetUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1262 <unnamed>:ShowUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1198
12/16 09:07:56.195      <unnamed>:SetAttribute()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1878 ShowUIPanel()
12/16 09:07:56.195      Interface\FrameXML\UIParent.lua:1862 ToggleFrame()
12/16 09:07:56.195      TOGGLEWORLDMAP:1
12/16 09:07:56.781  Global variable uncheckImage tainted by PowerAuras - Interface\FrameXML\UIDropDownMenu.lua:500 UIDropDownMenu_Refresh()
12/16 09:07:56.781      Interface\FrameXML\UIDropDownMenu.lua:568 UIDropDownMenu_SetSelectedID()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:661 WorldMapZoneDropDown_Update()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:1686 WorldMapFrame_UpdateMap()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:190
12/16 09:07:56.781      SetMapToCurrentZone()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:157
12/16 09:07:56.781      WorldMapFrame:Show()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1420 <unnamed>:SetUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1262 <unnamed>:ShowUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1198
12/16 09:07:56.781      <unnamed>:SetAttribute()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1878 ShowUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1862 ToggleFrame()
12/16 09:07:56.781      TOGGLEWORLDMAP:1
12/16 09:07:56.781  Execution tainted by PowerAuras while reading uncheckImage - Interface\FrameXML\UIDropDownMenu.lua:938 UIDropDownMenu_ClearAll()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:684 WorldMapLevelDropDown_Update()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:1687 WorldMapFrame_UpdateMap()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:190
12/16 09:07:56.781      SetMapToCurrentZone()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:157
12/16 09:07:56.781      WorldMapFrame:Show()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1420 <unnamed>:SetUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1262 <unnamed>:ShowUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1198
12/16 09:07:56.781      <unnamed>:SetAttribute()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1878 ShowUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1862 ToggleFrame()
12/16 09:07:56.781      TOGGLEWORLDMAP:1
12/16 09:07:56.781  An action was blocked in combat because of taint from PowerAuras - WorldMapBlobFrame:Hide()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:1634 WorldMapFrame_DisplayQuests()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:1690 WorldMapFrame_UpdateMap()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:190
12/16 09:07:56.781      SetMapToCurrentZone()
12/16 09:07:56.781      Interface\FrameXML\WorldMapFrame.lua:157
12/16 09:07:56.781      WorldMapFrame:Show()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1420 <unnamed>:SetUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1262 <unnamed>:ShowUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1198
12/16 09:07:56.781      <unnamed>:SetAttribute()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1878 ShowUIPanel()
12/16 09:07:56.781      Interface\FrameXML\UIParent.lua:1862 ToggleFrame()
12/16 09:07:56.781      TOGGLEWORLDMAP:1

Global variable uncheckImage is not directly referenced in my code. I guess this must be something to do with my check-boxes (I have a custom 3 way check-box)?

I am lost as to where to start solving this so any pointers gratefully received

Cheers!