[plt-scheme] lockups on tab switch

I've been noticing a problem that i think i just isolated.  When I
load several programs in tabs, then run one of them, and it's a long
computation that spews lots of debugging information out to the screen
as it runs, then switch to another tab while it runs, I get "send:
target is not an object: #f for method: get-parent".  At this time,
the display of the original tab is stuck in the middle.  attempting to
hit break gives "unit.ss" broke the contract
(case->
 (-> string? string? string? any/c)
....

Happens every time for me.

Corey