48SX and 82215A 128KB RAM card odd behavior

[cruff]

I have an 82215A 128KB RAM card that recently started causing my primary 48SX to behave oddly. The symptom is that the stack contents disappear across a power cycle, but the calculator is not complaining about invalid card data at power on (as it does when you remove or replace the memory retention battery). Simple stack manipulation and arithmetic work correctly when the card is installed. The other contents of memory seem to be retained, such as variables, but I haven't filled memory completely either to see if something else might be disappearing. This happens regardless of if the card is merged or not. Physically removing the card results in normal behavior. If I recall the memory layout correctly, variables are kept starting in the on board 32KB of memory and the stack starting in the expansion cards when they are merged.

My first thought was a battery issue. The card's battery was at 2.9V, and a new battery (3.2V) does not change this behavior. The calculator's batteries are at 4.5V. Do I remember correctly that while plugged in, the calculator will supply power to the RAM card when the calculator is off?

Oddly, when I test this same card in my spare 48SX, everything behaves normally in my limited testing. My primary 48SX also behaves itself when a TDS 256KB RAM card is installed (but of course the 48SX can only see half of that one).