bug: SL CPU usage at ~25%/50% when minimized

Steps to reproduce the bug: Open SL, minimize it (don't just alt-tab to another app with SL's window underneath), and check Windows Task Manager to see how much CPU SL is using.

Observed results: ~25% CPU usage on a Pentium D (dual-core) 820 CPU (which would be ~50% on a single CPU. Previous SL versions (not sure if it was during preview testing or SL 1.9 before it) reduced CPU usage to 0% when SL was minimized.

Expected results: 0% CPU usage when SL is minimized