Quote Originally Posted by SMD111 View Post
the additional effect of enspells takes priority over and does not stack with any other additional effects that can possibly be proc'ed, including additional effects directly on weapons or from Sambas.

http://www.bg-wiki.com/bg/Category:Enspell

this has always been the case
that was actually changed awhile ago. Excalibur will proc its additional effect instead of the enspell.