So are you saying that is repeatable with HomeDiskFree? And removing HomeDiskFree stops it completely?

When it gives the memory card in use message, does it crash immediately, or what actions do you take before it crashes?

You see, it (AFAICT) can't be catching an exception from that. If there's a problem, it'd seem to be with df, aka busybox. But I'd guess (without actually seeing it, and thus with low certainty) that the problem's elsewhere.