I noticed this bug few month ago: when I try to update track number/date/disc nub/total discs (but total tracks works fine) it just makes the field blank. I tried all available tagging plugins—same behavior. I figure out that in fact foobar writes these data in ID3v1 tag instead of v2, so if v2 is turned off and only v1 is present—it works fine and all fields are appearing in foobar's window. Please fix this.
Can you provide some examples of what you are entering into those fields?