If they're a miner or woodcutter as their civilian job it causes all sorts of mayhem.
Never found that to be the case, from .12 to the current release.
it happens when the job use the tool the dwarf has in hand as weapon, and there are no excess tools.
example: one axeman and woodcutter.
when becomes civilian, it get the 'pickup equipement' job. but it fails, because there are no usable axes left - the only one is in his own and so he doesn't 'see' it (it's tasked or something)
so he could not become a wood cutter anymore.
if an axes is produced, he will pickup that and go along happily thereafter. note that after the ax is swapped for the other one both are 'claimed' by that dwarf and unusable by others.
so if there is another dwarf in the same situation he could not use the ax left over by the other one.
same with hunters and xbows.
using non conflicting tools works, but dwarves won't carry them both, swapping between them at each draft, losing ton of time.