Most likely that or short-term disability, neither of which are shameful (not that you implied that they are.)
The real problem is that a competent manager would have transferred the work to another dev.
Maybe the system is byzantine that only this guy understands it well enough to make the change.
Yeah, that's likely, but it's also a terrible sign of mismanagement.
I once worked at a big company that had literally one guy that understood the single sign on system.
If that's the case, then that should be the real story. What if the guy gets hit by a bus, then the issue will never get fixed.
I think the OP didn't mean the guy's leave length, but a bus factor = 1 of the project
Any or all of the above. If you find yourself making the statement "we couldn't fix your bug because the developer was on leave for six months" then there is something mind-bendingly wrong with your world. Six months is enough time to hire another developer to fix the bug (even if it's a temp because they're coming back). You don't just... leave it broken for six months.
Well, apparently you do.
Mismanagement in the department of corrections? That's unheard of! Especially for their IT infrastructure.