Using Arduino Uno instead of FTDI cable to program 1284p w/ Optiboot

[system]

ghps:
The interrupt problem is even worse: No matter which interrupt I use, attachInterrupt defaults always to INT0 on pin 16/D10 - which is now used for RX1 on UART1. So in fact one only of the three interrupt lines is usable.

This assertion is backed up by what code?

Sorry false alert: The interrupts work as they should.

And one should never mix development environments: After one hour of testing I've found that using the sketches from Eclipse directly in the Arduino IDE caused avrdude to upload the same sketch again and again...