Forum Moderators: phranque
More-than-likely it is collapsing an empty cell. May sure all td's have at minimum a in them to keep NS from do that.
Else, run the page through the W3C validators [validator.w3c.org] and look for some common errors.
.ps, if you can't find this post in a few days, look in the browsers/html forum for it. I'll move it there.