RS232 buffer not clearing after reset, Fanuc 30 series

[LockNut]

This is a problem I haven't seen yet. 10 machines, most 31i series, a couple of Oi's. Some of the 31i's, during drip feeding, will not clear the buffer after hitting reset-edit-reset. This is causing occasional crashes and other problems with inexperienced operators. Has anyone seen this? And if so, what was the cause. There are no obvious differences in the parameter settings, the normal ones at least. All machines are set the same way and are fed from the same computer.

Thanks in advance,

Paul