Aslak,
I performed the test as you asked, and you are correct! If I disable broadcasting on start, and don't allow any BLE traffic, UART ISRs work just fine.
So now the question is...
Will this be fixed in v1.3, or is this a physical limitation of the stack + chip, and therefore some clever semaphore trick is going to have to be used to ensure both the radio and uart ports don't talk at the same time.
I'm hoping this will be fixed, otherwise this could cause some major problems down the road.
Thanks!