Quicksilver goes straight to text-entry mode
If I recall, there's a QS trigger called something like "Command Window In Text Mode."  Go to Quicksilver>Triggers>Quicksilver, I think, and look at what triggers are enabled.

Another possibility is that you have the "Spacebar Behavior" set to "Switch to text mode" in Quicksilver>Preferences>Command, and this is getting triggered when you use cmd-space.  It shouldn't matter, but it's worth a look.