For View->Perspective->Debugging I have GDB/CDB debugger:default. Yes, when I start debugging it switches to the debugger. I'm running 12.11
If you change the perspective, while it is active (the debugger is running or you switched to it manually) and switch back to another perspective (agian automatically at thje end of a debugging seesion, manually or on close of C::B) you should get an annoying dialog, that asks you to save the changed perspective.
You might have turned this off (for this dialog).
To turn it on again, you can go to "Settings -> Environment -> Disabled dialogs" to turn it on again.
You can also save the perspective manually.