I can't confirm this, but multiple people are reporting it so I thought I'd put it here for reveiw:
http://www.purezc.com/forums/index.php?showtopic=51698&st=0&#entry738235
Apparently somehow strings are getting shifted in index, with no way to reverse it but to re-enter/re-number them. Like I said, I can't confirm at this time, but it would certainly be a huge hassle for a quest designer. I know this is very vague, and it's unlikely that it has an obvious error, but perhaps some little-used function references the strings in an unusual way?
So, just to be sure I understand it, the bug is that for each Screen in a quest, the Message String setting is suddenly set to 1 greater than what it ought? Hmm.
Does this mean that the strings themselves in the list are unchanged? So that string 2 still has an ID of 2, etc?
I wish I could answer those questions, but I'm not sure exactly what steps the users took to get the results reported. I'm anxious to try our the newly revised system though, it looks promising!
We can't be certain, but _L_ changed how string deletion works, and I bet that fixed this problem.
I'd be willing to bet that it has fixed it also.