This is what the general consensus on the amanda-users list has been for
some time now. Linux ext2 dump/restore is massively broken.
I believe that ext2 dump on a mounted file system in Linux is pretty
much deprecated, though it should still work ok if the partition is
unmounted. It's not dump's fault and it's not something that dump can
fix. The design of the page and buffer caches in the 2.4 kernels
makes it impossible for dump to see the correct versions of some
files. (Strangely, my tests suggest that it's files written without
O_TRUNC that are handled incorrectly.) And no amount of waiting or
syncs will help.