Disappearing plug-in panels in MU4

VST instruments and some Audio FX now work quite well in MU4. For an effect like Reverb, a panel like the one shown here may appear in the MuseScore window.

However quite frequently these modest panels disappear, and then to get them to reappear to make changes it is often necessary to select a different plug-in or effect, then reset back to the original one.
Is there a reason why these panels suddenly become invisible, and is there any way to control their visibility so that the clunky reset process is not necessary?