I went ahead and posted a ticket for this (I just threw the URL for your post into the body of the ticket) so I don't forget. This seems symptomatic of similar issues we've seen reported since around July.
local colcount = tooltip:GetColumnCount()
local lineNum = tooltip:AddLine( " " )
tooltip:SetCell( lineNum, 1, "short", "LEFT" )
tooltip:SetCell( lineNum, 2, "short", "LEFT" )
lineNum = tooltip:AddLine( " " )
tooltip:SetCell( lineNum, 1, "quite a lot of text that exceeds total width of the two single cells above",
[B]nil[/B], "LEFT", colcount)
The bolded part is unnecessary, and is probably throwing things off.
From that list, the only AddOns that actually uses LibQTip is AckisRecipeList and Collectinator. Also, LibQTip does not utilize the GameTooltip - it mimics it, so no line modification is happening. What tooltip AddOn are you using? How are these AddOns disrupting it?
I'm still not clear on exactly what you're trying to describe or how LibQTip is effecting your tooltip AddOn.
@jokeyrhyme: I declined your ticket for setting colors in a range (including the gap between columns), but the latest release should provide some relief - there are two new functions: tooltip:SetCellMarginH() and tooltip:SetCellMarginV() - if used, it must be done so before the tooltip has had lines added.
You should probably also consider that people who are using TipTac (or another addon) to modify the appearance of tooltips are probably using it because they want their tooltips to look a certain way.
While this is normally true, the way the GearScore author is using LibQTip is as an information panel anchored to a frame rather than as a tooltip so the scale change is undesirable and the backdrop change may be as well.
I just added your code to his lua in the appropriate place. All it does is set the scale of the tool tip. It has the same effect as if i set the scale in tiptac except that it only effects the tool tip in the database which is where I inserted it. In essence if you looked at the skill score missing thread where I adjusted the scale in tiptac it does this but only to the database and not all game tips. Here is the problem tiptac is firing off first and then qtip is grabbing that altered tip and using it for gearscore. which screws up gearscore is there a way to make qtip Acquire the game tip FIRST maybe that would fix it.
You need to add that call to every place where he uses LibQTip:Acquire().