How come you can't reset no mod scripts any more?

I have a LOT of vehicles, mostly planes. Some of them have had problems with changes in sim boundaries, or with changes in the way animations work, and I've been able to get them working after they've started spamming me with script errors by resetting all the scripts.

Recently I discovered I couldn't do this any more. You can't reset no-mod scripts in no-mod objects.

Is this a bug, or a feature? If it's a feature, why? There's no risk of loss of intellectual property here because resetting a script doesn't involve downloading it (or if it does, that's a bug).