Hi Marc!
I am using the "original" theme. Maybe it's the surrounding CSS applied to this table that does the bad effect.
Okay, now I see. Sorry for not getting your intention in first place.
The reason why the fields are not in the same row is because of whitespace wrapping. As the browser thinks he can put a linebreak between the input and the label element, and the table is already very large, it will wrap the two elements.
The only thing you can do about this is to add a <div style="white-space: nowrap">...</div> around the checkbox and label so that a browser will not cut them into.
HTH, Garvin