Simplejackit

okay this is a magic trick that works for alot of weird things that happen from importing dae files into sl.... so in blender, take your model and export it as an OBJ file... then re import the OBJ back into blender... then export that obj model you just imported as a dae file... then import into second life. idk why exactly this fixes it.. but this has worked for me on a few different issues including one very similar to the problem you are having