Hmm, according to the wiki:
http://nwn.wikia.com/wiki/Mass_charm Quote:
This spell only affects humanoids, even though its description says "creatures".
Quote:
The in-game spell description states that this spell lasts one round per level, but it actually lasts one round per two (caster) levels.
The scripts are still mostly bioware default, so this is not really a bug more a feature request/change.