* if a block's first four bytes consisted of the JFS_MAGIC_NUMBER (0xc03b3998), these bytes were replaced with zeros when the block was written into the file system's journal. If the file system was subsequently recovered, a typo, associated with the Linux Journaling Block Device (JBD), could result in data corruption on recovery. The Linux kernel typo has been corrected but the fix was not carried over to e2fsprogs, where the equivalent problem could present during an e2fsck log replay. It has now been carried over and data corruption will not occur in the circumstances described above.
Note: the data corruption potential was always low. It is unlikely ext3 metadata blocks will ever contain the JFS_MAGIC_NUMBER in their first four bytes and the "data=journaled" mode is rarely used.