Actually, I just took a look again, and I have apparently tweaked Kivan's DEX (didn't seem right to me that an archer didn't even have an 18). Now, this is odd, because I'm almost positive that I did this *after* the playthrough I'm having issues with, and changes shouldn't be applied retroactively, should they?
Anyways, the problem is not that I'm trying to improve his AC (the -12 is from my final ToB save, so this is as good as it's likely to get), it's that, while there are better bows, there is a stretch of the game for which Kivan's bow is usable, but I'd like not to lose (or gain, rather) that one point of AC when I replace it with a different bow.
Kivan's base AC is 6, and it's true that, without any other gear, the bow doesn't keep raising his AC when unequipped, so Miloch could be right on that one. I seem to have narrowed the problem down to Montolio's Cloak (Cespenar-crafted item). When I remove it, the bow does what it should be doing (lowers AC by one point when equipped, raises it back by one point when unequipped, and the raises don't cumulate). When I put it back on, the problem reappears. I loaded an early ToB save, where I didn't have Montolio's Cloak yet, and sure enough, the bow behaves normally.
Stats for Montolio's Cloak:
+1 bonus to AC
+1 bonus to all saving throws
+2 THAC0 with off hand
There's also an added oddity: description says that it's only usable (or rather "usuable", seems to be a typo there) by Rangers, but Coran is also able to equip it, despite being a Fighter/Thief. Further testing reveals that Jan and Haer'Dalis are, inexplicably, also able to equip it. No one else, though. Well, except for Minsc and Valygar, but that's normal. I'm unable to test Korgan, Anomen or Edwin, however (due to never having had them in the party).
Edited by Nilfalasiel, 22 December 2011 - 04:44 AM.