Sounds like a balancing problem to me. Have you tried exchangig the blades - say blade A in the B position and vice-versa ?
When using any depth gauge, you should make VERY sure, that the cutter positions are identical when gauging. This is easily overlooked but very important.
Did you have the blades sharpened or sharpened them yourself ? Sometimes one of the blades is ground deeper to get rid of a nick. The other blade ( even if not nicked ) should be ground down the same amount to preserve balance.
Simple measures which I'm sure you already knew, but perhaps this can be of assistance.
Regards,
Job
Edit: This can also be caused by replacing a blade mounting screw. Sometimes when you chance blades you loose a screw - it happens. Rather then getting the screw back from the intestines of the machine, a similar fitting screw is used. This may upset balance for it's unlikely that the replacement screw is the exact same mass. This may seem like splitting hairs, but especially in a table planer where the mass of the head isn't as big as in a large stationary planer AND the bearings are less robust, it may well pose a problem.
