Problem is I don't have a replacement...
About the driving/oscillator problem mentioned above
It looks like a HC-49 type package, 10MHz, parallel mounted with 2 22pF caps. It replaced a similarly packaged but a lot more battered, presumably 8MHz crystal (the writing on the case wasn't that readable but probability seems to indicate it was a 8MHz one). As far as I understand (both crystals and oscillators are kinda' mysterious to me at the moment) there's no powered oscillator to talk about. The dev-board I'm using is a EasyPIC4 by Mikroelektronika.
Furthermore there's quite some way from the crystal to the osc1 osc2 pins, and there's 2 jumpers in between. Could it be the work of stray capacitances across the board, from under the board, or EM interference (working in an office of an electronics/automation/IT/C firm, who knows what kind of noise I'm getting)?
Added after 1 hours 2 minutes:
I've been working on the board this morning for an hour and a half... The problem hasn't resurfaced... Serial comms work smooth, and the LCD displays propperly...
You know, I kinda' wish it DID resurface, 'cause this is just kinda' too annoying...
It's not that I'd believe in some supernatural explanation, and that would make the whole occurence mysterious or something... It's just that the darned thing got me started on trying to "fix" it, or finding out what causes it and now it just... left... The nerve...