The remote is based on the Home Theater Master SL-9000 (the version that came with the 950 is lacking the LCD screen). The manual's remote is available on the web, here's a copy of the manual from amazon.

My first thought was that the previous owner may have programed "volume punch through", so the remote is trying to change the volume on some other component. I did a search for "volume punch through" on the Outlaw board, and came up with a bunch of deleted threads. Plus this old thread about punch through. In it, gonk explains how to set the volume punch through (from page 23 of the SL-9000 manual).

If this doesn't work, you could try a more drastic solution: resetting the entire remote. On page 18 of the manual it says to "Erase All Buttons in All Device Modes" you press and hold the TV Device Button and the LIGHT button simultaneously, for approximately ten seconds."