CM10.1 with Go Launcher sometimes shows Trebuchet

[KlunkUK]

I have installed CM10.1 on my SGS2 along with Go Launcher. On the whole it works fine and Go Launcher looks and acts as expected. However when I get an email and I read it through the notification bar hitting the back button always takes me to Trebuchet and not Go Launcher.

Any ideas why this would be happening? I dont think I changed the notification bar, could that be the cause?

Thanks

KlunkUK