So the problem is in the display, not the actual amount that's being given right? That's not so much that it's not a bug so much as we don't care because its just a display issue. I'd urge you to turn off that xp display anyhow, which many of us do which is why this is probably still a bug, because not only does it tend to be inaccurate but it tends to overwhelm the amount of information that can be displayed in that tool tip help hover. That and, there's also, as Raxo pointed out, probably the intent by its original designer, just to show building sources and to show what more you COULD currently construct to help add to the total before you train the unit.
All that said, I get that it's frustrating that the GGs aren't tallying in there. I'm sure you can understand why that would be a low priority issue to resolve. It may even be 'on the list' somewhere having been reported before.
Maybe I'll look into making sure it adds in sometime soon though.