I've also been having similar problems with my 880/260 zigbee set. Have yours been affecting all devices or only some?

For me, I've noticed it being certian commands/devices. Significantly more common on learned/hex codes.

The only thing i have found to help was to try alternative codes for problem codes. Meaning, if you have a samsung tv, try similar codes from other samsung tvs.

EDIT: just to be clear, the 'problem codes' work perfectly by IR, and do not necessarilly cover the whole device. the main codes for my tv worked, but the discretes i found here would fail by rf only. Different discretes in the database worked both ways