AVR-Chat

I've tracked it down, but still it makes no sense...

It's the SEI instruction!
That's the last thing I do before hitting the idle loop.

Any call I make AFTER the SEI, ends up in this wierd place.
That means that it's almost certainly an ISR that's vectored to the
wrong place, but it's not jumping to the interrupt vectors and THEN
off to somewhere else. What happens is that it would appear that the
call should be a normal call, but the address it lands on is wrong.

Consistent, but wrong.

Wierd.