Problem anchoring GameTooltip

[alikim]

local function onMouseLeave(self, motion)
	GameTooltip:Hide()
end

local function onMouseEnter(self, motion)
	GameTooltip:SetOwner(UIParent, "ANCHOR_CURSOR")
	GameTooltip:SetAction(ActionButton_GetPagedID(ExtraActionBarFrame.button))
        GameTooltip:Show()
end

This works perfectly well on my custom button.

But I want this tooltip to show where most of them show up - around the right bottom corner. As far as I can see from ingame prints, while the gametip is on there, the anchor is set to "ANCHOR_NONE".

If I change the anchor to "ANCHOR_NONE" it stops working properly, the size of the box upon which the text appears is different every time it shows up and sometimes the text might not show up at all, just the box.

What I'm doing wrong here?

Thank you!