Gents-
I'm not sure it will help, and sorry if this was posted before (I didn't follow any linked threads) but I was doing some searches today and ran across a blog posting that has new core files for the 644P/1284P based on 1.5.6-R2.
The posting was at http://www.leonardomiliani.com/2014/core-per-atmega644p1284p-aggiornato-per-lide-1-5-6-r2/?lang=en
Just thought it might be useful.
Regards,
Brad
KF7FER