I've ran into yet another odd bug - one that I hadn't noticed until now, but it's actually been there awhile. All NPCs have the same spell - called brittlewind - and they can all cast it usually. Very annoying (because it's relatively powerful) and immersion breaking.

Anyone know how I can diagnose what mod adds this?

The problem is that Brittlewind was set to "autocalc" in Morrowind.esm. This is corrected by the Morrowind Patch Project (e.g.: "Morrowind Patch v1.6.4.esm"), but anything loading later in your load order could revert it.

You can try searching for plugins that define the Brittlewind spell using my command line program http://code.google.com/p/mlox/wiki/Tes3cmd:

tes3cmd dump --type spel --id brittlewind *.esm *.esp

Or, if you don't like command line programs, you could try a program that just does string searches like http://www.inforapid.de/html/searchreplace.htm (it's free).

Ok, that definitely fixed it. Thanks a lot And thanks for the links in your sig. mlox is great. As is MCP.