I discovered this after the graph window kept disappearing, forcing me to delete preferences and restart.

When you move a floating graph window around, a necessity with small screens, sometimes it will appear to dock itself but there's just an empty white box that can't be closed like the other windows. The only way to get rid of it is delete all graphs, but then if you make a new graph it will still reappear as a docked empty white box. The workaround is to go to the material tab and create a new graph there, then return to the pose tab and the problem is gone.