Oh...wait a moment.

Check you tuner's wiring connections. I saw something incredibly similar yesterday, but with the normal serial port. I was configuring a linux laptop to listen on the serial port (for kernel debug purposes) and when I toggled the Hardware Flow Control setting with the empeg connected, the empeg promptly went into shutdown mode, and also switched modes on me...I couldn't reproduce it at will though.

Since both the regular serial port's and the tuner connection's UARTs are built into the ARM processor, it is possible that they would have a common effect if something unexpected happened.

I'm not sure which of the standard RS232 lines the tuner port uses (aside from TxD/RxD)...but if one of them is badly or misconnected such that it is seeing a transient when it shouldn't then possibly this is the culprit.

The other thing that I should mention is that when I have my empeg connected to the laptop and connected to my workstations line-in at the same time, I can hear a ground loop. Annoying, but I can live with it for the occasions I need to debug serial output. But - it might be that the serial ground on the laptop is far enough from the empeg's logic ground to cause transient glitches that could possibly trigger such behaviour.

I wonder if somehow there is a groundloop from your antenna that could be having a similar effect.

A lot of 'ifs', I know. But it's too much of a coincidence for my liking.