Reported by Nikolaus Schaller, Aug 27, 2010

/dev/mtd3 should be a jffs2 formatted file system (since it is quite 
small for yaffs2).

Unfortunately, the automounter for the root-file-system can't 
distinguish between yaff2 and jffs2. So it falls back to yaffs2 and 
destroys the jffs2 file system.

Solution:

I think just add fs_names_setup("jffs2") to F3 key mount. 
(arch/mips/jz4730/board-minipc.c)