When you are busy you are meant to not receive any toasts, however if you have a POP3 email check set-up through MP!L you still get the toast. I checked and you have it correct with scripts however and also when it comes to Event Notifications. Patches, why aren't you saving code and using a single function for all toast creation? If you did then you wouldn't run into little problems like this.
* markee runs from Patchou
PS. Would be nice if the testers caught bugs like this in 4.50.... let's hope.
* markee runs from the testers