I think problem is in a patch of this changeset:
https://dev.openwrt.org/changeset/13708 ... i/patches/
In this changeset, many patches from trunk were merged in 8.09.
So, the first attempt could be:
try openwrt compiled from branch 8.09 with 13707 revision;
if problem is present I'm wrong
If not, try openwrt compiled from branch 8.09 with 13708 revision;
if problem is present, the bug is in one or more patches of this changeset. Else we must look in other later changesets.
Could you make this test?
If you don't know how to compile openwrt (or you haven't time to compile), tell me and I will compile the 2 different version for you.