Multiple field groups

When adding a CCK field, one has to create a fieldgroup to allow vertical tabs to work with the CCK field.

This works (in my case) when creating a single fieldgroup holding only 1 CCK field.

The error occurs:
- when adding two CCK fields to a fieldgroup: only one CCK field is shown
- when creating another CCK field group, the second field group does not appear on the vertical tabs checkbox selection, nor is it actually shown on the vertical tabs when editing content.

The error is independent of field-type. I tried to create an identical field type, part of a second group. Where the exact same group shows up, the second does not.

Is this a know issue?