Sony KP-61XBR48 Service Menu Item Keeps Changing

I have a Sony KP-61XBR48 RPTV (4:3 standard NTSC model), purchased in 1996, that is still in good working order except for two recent problems. 1. One item in the service menu (not the user menu) sometimes changes its setting after the TV has been turned off for several hours. Specifically, the service menu item that changes is called "SPIX," which I believe controls the sub-picture (contrast) range available on the user menu. When I write the service menu change to the TV?s memory, sometimes SPIX will still change its value after the TV has been turned off for several hours. No other service menu items are changing settings on its own like SPIX is. 2. When I am in the service menu, the TV?s picture is different (color, hue, brightness, contrast, etc.) than when I am not in the service menu, making service menu calibration adjustments difficult. Does anybody have any ideas what could be causing these two problems and how to fix them? I appreciate any advice and suggestions you may have. Thank you.