GameTooltip leaving screen

[Lybrial]

When I start the game at first everything is fine regarding the GameTooltip.
It is showing perfectly and always sticks within the screen, so it never leaves it
so that parts of the tooltip are cut and not readable.

But as I play along, some actions seem to happen which make the GameTooltip
leave the screen. For example:



I know that there once was a bug at blizzard code which caused that. Is that still the case?
I also know that addons can cause such things.
Any ideas what could lead to a GameTooltip leaving the screen?