Weird issue with Pioneer AVR volume control

I have a recent Pioneer AVR (not Elite), long out of warranty.  No issues whatsoever for over four years until now.  Just the other day, for no apparent reason, the remote volume control has reversed.  Raising the volume via the remote (both a universal and the OEM remote) lowers the volume.  Lowering the volume via remote raises the volume of the AVR.  All other functions seem to operate normally.  Any ideas?  TIA. 
Unplug it from the wall for a while, then plug it back in.
Once you unplug it, press several of the buttons on the front of the unit several times.  This will drain out any lingering capacitance that might be left.
Thanks, mofimadness!  Worked like a charm. 
Sweet!  Glad to help.