Aaron L said:According to Libris Mortis, the souls of those raised as undead, even unintelligent undead, are indeed trapped in the undead shells.
Do you have a page number for this? Your claim seems to contradict what I'm reading in the book.
From page 7:
"Evil acts can resonate in multiple dimensions, opening cracks in reality and letting the blight creep in. A sufficiently heinous act may attract the attention of malicious spirits, bodiless and seeking to house themselves in flesh, especially recently vacated vessels. Such spirits are often little more than nodes of unquenchable hunger, wishing only to feed. These comprise many of the mindless undead. Sometimes these evil influences also manage to reinvigorate the decaying memories of the body’s former host. Thus, some semblance of the original personality and memories remain, though the newly awakened being is invariably twisted by the inhabiting spirit, resulting in an evil, twisted, and intelligent creature. However, this being is not truly inhabited by the spirit of the original creature, which has left to seek its ultimate destiny in the Outer Planes. This amalgamation is something entirely new."
The emphases were added by me; it's saying specifically that for many of the mindless undead, the animated spirit is not, and has nothing to do with, the original soul. It goes on to say that in some cases, souls can be trapped within their corpses by evil spirits - but this isn't the rule.
The only unifying definition of undead is that they were once alive and they're empowered by negative energy. Many undead specifically do not have their original souls.
Unless there's some other note in the book that I'm missing, I'm guessing you're simply mistaken on this one. If I did miss something - and I may well have - it seems there's a contradiction in the text.