Please explain bbt_create (problems)

[Andriy Korud]

Hi, 
I'm trying to understand how initial bbt_ceate works? 
I have NAND chip erased for jffs2 (flash_erasall -j) with some data in OOB (jffs2 clean masrkers). And bbt_create() calls check_pattern() which compare each byte with 0xff, in my case comparision fails (jffs2 cleanmarker != 0xff) and I have every block marked as bad.
Should not check_pattern() checks only byte at 0x05 in OOB (according to http://www.linux-mtd.infradead.org/tech/mtdnand/x255.html )? 
Also is it possible to scan chip for bbt starting from certain block (not 0) without dirty changes in mtd code?

Thanks in advance,
Andriy Korud