I would say fix it where possible. I can't imagine a situation where someone would purposefully write a condition with side effects as a secondary condition with the intent that short-circuit evaluation would be ignored, or more importantly, any situation where that would be needed. It's far more likely that there are scripts that are taking performance hit from the lack of short-circuit evaluation, and could potentially be causing bugs. The random loot in KOTOR 2 overflows the stack if you spawn too many items at once, for example. There could be more intensive operations, like in the AI, that could potentially be causing problems. Maybe that would even account for bugs such as creatures randomly not attacking in the middle of combat.
I'm certainly worried I might've written code under the assumption that short-circuit evaluation would be obeyed. I suppose if that's true, I could invert the logic to use && in the meantime, since that does seem to short-circuit properly.
I'm almost afraid to ask, but does NWScript have a goto statement? I haven't seen any example of it in code, or any reference to it, so I assume not.
Oh, I hadn't seen this one before, but I've seen problems like it. It's understandable considering that not all the developers were computer scientists, and even designers like David Gaider and Chris Avellone did incidental scripting to take some of the burden off the programmers, but the downside to that is not everybody necessarily knew what they were doing. Plus the one you quoted looks like it might've been a copy/paste error, considering that it's only the last branch that's wrong. Stupid mistakes can happen to anyone.