Was just perusing the Rockbox forums, saw this from one of the active developers about the port to Sansa Fuze (and other AMS models)
For users with 8GB and more models : don’t use test builds because they could totally brick your Sansa.
We don’t switch banks in SD transfers when we are crossing a bank boundary, so when crossing the 4GB border, we could accidentally write to the first blocks of internal storage, which hold the Original Firmware.
I noticed this problem when reading ata-sd-pp.c which has a comment line 951. (And by the way, it could be a source of the filesystem corruption the people using Sansa e200/c200 are seeing).
An efficient fix should be relatively easy to do and also applied to ata-sd-pp.c, but in the meantime be careful!"
Emphasis was his, I just copied/pasted.
Once again, and I’m sure I’ll take heat for it, loading up a development build of firmware on your device is NOT a good idea, unless you’re contributing to the development of said firmware. If you fully understand you can turn your functional DMP into an ineffective doorstop, fine.