CCK Fieldgroup Tabs & Multigroup browser compatibility issue

First thanks for the great module!
When applying the 'Tabs' style to a Multigroup, and displaying the subgroup format as a table (single or multiple columns), the tabular data (cck fields and labels) are displayed well only in Firefox, but not in IE 6, IE 7 or Marathon.
I think that it's a CSS issue, but I couldn't locate exactly where the problem lies.
Any ideas?