Stacks Hiding Behind Backdrop?

[katir at hindu.org]

is anyone else experiencing the annoying "winking out" of stack stack behind a backdrop that has been set?  

Scenario is: set the backdrop to black, open a Rev stack. then open mail.app on the mac. do some emails, click on the Rev stack to activate and it suddenly disappears. Actually it is open, but "jumps" behind the background which acts like  an opaque layer such that the stacks underneath cannot be seen unless you chose the from the window menu. This is quite annoying.