I actually have the same thing, and it also happens with advanced interface switcher. So it isn't caused by the apps, but rather by something underneath.

The only way I manage to switch without the reboot, is to manually disconnect from WiFi first.

So if I'm on WiFi and want to disable that, I first force the connection to GPRS, and then disable WiFi.

note: using modified kernel from titan, but posted already about this in his thread - no one else had this issue there.