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.