Unfortunately I have noticed now [3.08] that when I am in action groups window I am able only to grab and move an action or group of them using mouse all the way only in the up direction - i.e. the list will scroll itself thus allowing me to move all the way only to the top. Because when I move down while holding an action or actions there will be no automatic scrolling happening. And so when going down I have to revert to the old method of using the triangle icon located at the right bottom corner of the action groups window
I have just checked this once again, wanting also to take some screenshots. And that bug was still there - but by accident I made it go away. How?
Wanting to make a not-bloated-with-irrelevant-data screenshoot I resized vertically that window of Action Groups by making in shorter - previously It was taking a 3/4 of my vertical space. Also after making it once again so tall as it was, this bug was still gone
Because of this experiment
I was "forced" to choose sizes of all of the various Mp3tag windows [for Export feature, for Columns etc]. And so I was resizing them a lot and making also all kind of old and new adjustment to my configuration. All in all I must have hit some combination that brought that bug to life. And so I'll bet that somebody someday will report the same problem - but for now my Mp3tag seems to be working A-OK