[Vrul]

In addition to what jeruku said, you aren't parenting the entries to the scroll child to begin with. You are also repeating a lot of code when it could be avoided:

tab.ItemScrollFrame:SetClipsChildren(true)
 
local numButtons, lastButton = 0
for key, item in pairs(namespace.searchResult) do
    local buttonName = key .. "Button"
    local button = CreateFrame("Button", buttonName, tab.ItemScrollFrameChild, "OptionsListButtonTemplate")
    button:SetSize(192, 10)
    button:SetHighlightTexture("Interface\\BUTTONS\\UI-Listbox-Highlight2")
    button:SetText(item.name)
    if item.slot then
        button.tooltipText = item.itemType .. ", " .. item.slot
    else
        button.tooltipText = item.itemType
    end
    button:SetScript("OnEnter", OnEnter)
    button:SetScript("OnLeave", OnLeave)
    button:SetScript("OnClick", OnClickItemFrameButton)
    if lastButton then
        button:SetPoint("TOPLEFT", lastButton, "BOTTOMLEFT", 0, -1)
    else
        button:SetPoint("TOPLEFT", 4, -4)
    end
    numButtons, lastButton = numButtons + 1, button
    tab[buttonName] = button
end
 
if lastButton then
    local width, height = lastButton:GetSize()
    tab.ItemScrollFrameChild:SetSize(width, numButtons * (height + 1) - 1)
end

I'm unsure what you are trying to accomplish with the "tab.buttonName" stuff unless you meant "tab[buttonName]" so that's what I changed it to, remove it if you aren't actually using it elsewhere.