Like in the topic, whenever I turn off my STe and there is a SD card in the UltraSatan slot, the card is blank. Activity LED turns on on UltraSatan for a few seconds immediately after powering off the Atari, and I know that card is clear at this moment. Afterwards some cards have just 0x00, others have FxFF, but all are completely blank, no garbage, just 0s or Fs. This happens only on the STe. On STfm it works fine. Whats is more interesting, when I powered STe from a Mean-Well power supply it stopped erasing the card (almost - it still happened occasionally, but once for a few power cycles, not every time). The modern power supply has less output capacity, and voltage falls more rapidly after cutting mains power off.
My STe is one of the early units (with a bodged TTL chip), but I have replaced CPU to HC version, and MASK-ROMs to Flash memory.