Not sure if this issue is Unity specific, but I have tried it in multiple themes, and with no theme (and no other extensions) loaded.

If you click the "Help" button present in many of the windows, on click it will display the "button_help_down" graphic. However, after releasing the button it appears to display the "button_help_hover" graphic, and doesn't revert to the "button_help" graphic.

Testing on Win10
FGU v4.0.0 Ultimate (2020-05-14)
5E Ruleset
New Campaign
No Modules Loaded
Any Theme or No Theme