Shattered Kingdoms

Jail cells aren't no-magic rooms. You just can't cast in them.

That's the same thing, except that no one "walks in" to jail, they get sent there through a script which doesn't remove spells as a result.

I'd like to know if this is considered a bug. When I used to surrender to the law, I'd cast DI/DH/infravision first, so I could at least keep track of the who list while I was in jail.

It's probably a "bug", but really a "feature."