Hi Larry!
Can get similar behavior under Windows. (so, i think it is a little bug).
When i move the RTPreview window upwards until the blue top bar of RTPPreview disappears
under the main PI window get a vertical sliding bar at the right side to move it back.
But, when i let the cursor in the top area of the PI toolbar for some seconds suddenly this
vertical slider bar disappears und i cant get it back, except with
the solution so far: Minimize an maximize the PI Window
this gets the vertical slider back.
The time between vertical slider visability and automatic(!) disappearance is usually as long
as the black popup explanation stays and disappears automatically.
Means i have the Cursor, without touching the mouse over for example the "Next Preview"
toolbar Icon.
It does not happen all the time but trying it 3 - 5 times gets the disapperance working
.
Gerald