Bizarre floppy drive behavior

I'm hoping someone can shed light on this. I picked up a couple of NOS Teac FD-50A-03 floppy drives with DEC badges on the front and have been trying to use them in various older systems with little success. Yesterday I sat down with ImageDisk on my duplicating machine and started digging deeper. These things are behaving very oddly. From what I read on the web, the FD-50A-03 is a single-sided, 96tpi drive that supports 250KB/sec data rate and spins at a conventional 360rpm. This seems nominally to be true, but... I created a reference diskette by formatting single-sided on a known good 1.2M drive at 300K/sec (to account for its 300rpm operation). This should be the correct layout for the Teac drive. Here's where things get weird: - If I configure IMD to treat this as an 80-track drive and tell it to read the reference diskette single-stepped, it can read even numbered tracks only. The odd number tracks all throw read errors. - If I put IMD into alignment mode and select a track at even decade using the 0-9 command, it properly seeks to that track and reads it with no errors! Since this works for, e.g. 4-7, the drive clearly is a 96tpi unit. BUT, if I single step in either direction from an even track using +/-, it tells me it's seeing data from a track that's _two_ steps away and reads as if it was slightly out of alignment. If I try to move back to the even decade, that is now off as well. Moving back to zero and trying a seek to that same track gets me back to a good read! - If I take a new, bulk-erased diskette and try to format it 80-track single-stepped, it starts banging into the limit stop at slightly past track 40 - almost as if it were actually double-stepping. So, question is: What in blazes is this thing doing and why? Both drives behave the same way. If they're both defective, it's a rather odd defect. Steve --