Tired memory?

So I've seen an odd phenomenon on some older QBUS memory boards I've got in. I can't understand it, and I'm wondering if anyone else has i) seen it, or ii) understand the cause. What happens is that the _first_ time I plug them in, some don't work - some (maybe all, sometimes) locations are mangling the data (I forget whether it's dropped or picked bits). Oh, and we're talking 4164's/41256's (or equivalents) here, for the actual devices. However, if I let them sit for a bit (powered off), and then try again, they work fine! I first experienced this phenomenon on some M8044's, which have on-board electrolytic filter caps, so I was guessing it was caused by some sort of noise caused by the caps not working, and after a little while powered on, the caps reformed, and things started to work. However, I just experienced the same phenomenon on a Clearpoint DCME/Q4E board - which doesn't have any electrolytic caps on it. So that can't be it. Anyone have any clue what's going on? (Oh, and of course, for others - if you buy and old memory board, and it doesn't work... don't immediately put it in the 'bad' pile, wait a bit, and try again. You might be seeing this.) Noel