New optiboot; beta testers welcome...

westfw:
Yes. In newer compilers, PROGMEM handling is changed significantly. And linux installs the compiler separately from the Arduino IDE, so which version you have is pretty random.

I'll take a look and see if I can come up with changes that work for multiple compiler versions...

Yup, 4.6 changed the handling of progmem significantly, and all for the better. It's easy to make the changes, and they still work with older toolset versions. Basically, we have to stop using prog_types and make all progmem variables const (which they should have been already).