This absolutely smacks of hardware failure.
Its not possible for an error to span both the original firmware, and Rockbox, and have it not be so (to the extent of my knowledge). That's not to say that it wasn't caused by Rockbox (sure, this is possible) but this is a risk that comes with the project itself. Even releases aren't guaranteed to be free from error, unusable/unstable/git HEAD significantly less so.
[Saint]