Only thing that comes to mind is a problem I had with a DMX variety. Wouldn't switch to vertical polarity until the LNB voltage went below 13.9 - 14v. Otherwise it was stuck on H as the 'V' voltage out of the receiver was 14.4. Sorta fixed with a 'work around' of a diode in line with the LNBF. Think I paralleled a cap across the diode of around 600 to 1k pf. Just mounted a couple of "F" splices in an aluminum box and stuck the diode leads into them on the inside of the box. (Band side of diode to the LNBF) Diode drops 7/10 volt, so LNBF got 13.7 or so. viola! Other than that I'm stumped.
Maybe, more details, like regular blind scan or Detailed Scan (Think that's what they call it in the microHD)
Try it with the LNBF connected directly to the receiver?? (No switches/diplexers)