I’d have to do more digging than i care to at the moment, but there was a patch note at some point where they changed a value of an ability tooltip, and said it didn’t change the actual combat value, and that it was a fix of the tooltip only.
There has also been reports of some weapon tooltips showing strange numbers on the french client … while not an ability its the same idea behind it.
EDIT: found easier than expected. So here is the Tooltip fix from the patchnotes
- Fixed an issue which caused the damage displayed in the tooltip for Ice Beam to be modified by the wrong types of bonuses. This only affects the tooltip damage and not the actual resulting damage.
And since i mentioned it, here is the gear tooltip error in french
So i stand by my assumption that the tooltip does not affect the damage directly. The two are likely calculated separately, and that is where tooltip errors happen. One would have to check with actual damage outputs to be sure.