Ubuntu Atl-Tabbing on not works when Squeak is in full screen mode

Hello,
Squeak becomes like shell on Ubuntu 10.10 when it in full screen mode.
User cannot AltTab to other task. Tried this with Squeak's
Seaside3.0rc image with trunk's updates loaded. Me thinks this is a
bit weird. Sorry I can not fix this now, just reporting.
regards,
Vaidotas