256 colours does still cause trouble with transparency - Audacity triggers a box around the mouse then instead of creating a hand-symbol

We lately found Audacity transparency improved with 32bit colours.
With 256 colours depth we still see horrible stuff:

This test was executed on VBox 4.3.40 with default graphics driver.
0.4.6RC1 affected.

react.log
reactOS-0.4.6RC1.webm

Yes the display is immediately broken when I switch to 256 colours, right.
But it's Audacity process that reproducibly triggers that box around the mouse cursor then.