Oh sh*t, I thought my recent experience was just a quirk, but now I'm worried.
The SD75 I left for my parents at their home was completely dead when I checked on it this past week, despite the fact that I knew I charged it up.
I figured they used it and didn't charge it yet. I plugged it in and the charging seemed to work, though, unlike yours. However, I also think I put protected Panasonics into this (and can confirm in a few days), so now that would mean the protection circuit saved it if there was a defective short or something funky going on in the battery carrier.
Overall, I can't call this a great light or a smart purchase because these torches been experiencing one problem after another. I would be even more pissed if they are now ruining batteries and are a safety hazard.