Sorry missed this part earlier, no, that wasn't the problem, since the checksum error would always be logged in the syslog, and if I tried to copy the file locally I would always get an i/o error, with SMB (and aio read enable) it would still copy successfully despite the checksum error.
BTW, just did a test on beta30, with aio enable, and it's behaving correctly, i.e., a file with just a single sector corrupt will fail to copy, tried 20 times, and always got this:
At the same time a checksum error is logged (before only this part happened):
So that issue appears to be fixed.