@ps67:
Huh. A quick highly scientific (^^) test based on a single DRM-free ePub (as I mentioned, I don't read ePubs, so it's my only goto test file, and my Kobo is not linked to ADE ;p) revealed that I couldn't actually reproduce that behavior (on an H2O).
In any case, killing the RMSDK is a sound decision, and it may actually help with this, so:
https://github.com/koreader/koreader/pull/6179
(Plus, 75MB of RAM, wheee!).
EDIT: Ah. I wasn't using the latest Plato release, which probably explains it.
https://github.com/baskerville/plato/pull/116 ought to fix it.