Quartz
Hero
The SRD indicates that they stack:
I'd let MWM stack for all single-ended weapons which deal multiple types: dagger, halberd, morningstar etc. Double weapons are a different matter. The point is that a successful attack is a telling blow, not an actual hit.
As for the question of overlap vs stacking, I'll point out that combat feats normally stack with each other.
SRD said:Some weapons deal damage of multiple types. If a weapon is of two types, the damage it deals is not half one type and half another; all of it is both types.
I'd let MWM stack for all single-ended weapons which deal multiple types: dagger, halberd, morningstar etc. Double weapons are a different matter. The point is that a successful attack is a telling blow, not an actual hit.
As for the question of overlap vs stacking, I'll point out that combat feats normally stack with each other.