Well, the problem's back - I'm using the 1.12.267 build now, and the problem occurred on two different MX850s over the past week ... one was an existing one I was updating, that's been in use for >1 year, the other was a *brand new* one. Note that the error occurred on the brand new one on the _very first_ download, too!! More to the point, this brand new one had an MXF config built from _scratch_ (that is, not based on any exported config data from previous MXD/MXF files I may have used).

Ach, this is an annoying issue - I'm not ready to abandon the 850 yet (it's form-factor and more LCD buttons is better for some of our clients), so I really wish URC could identify & resolve the root cause here.