Unfortunately, in order to take this completely seriously, you would need to be able to verify that the problem still occurs *without* the heavily modified hardware. The adapter plate has the potential to introduce all sorts of weirdness (the fact that at least one other user I am aware of reports that *only* Lexar cards work in these adapters is very telling in itself and points a damning finger in that direction).
The issue absolutely smacks of a corrupt filesystem, and if this adapter plate is repeatably causing such corruption, I'm not sure it would be a: a good idea, or b: possible, to work around the issue in Rockbox.
[Saint]