There was a bug in taper-5.1.1 when creating archives. If you made an archive with 5.1.1, unfortunately, you will have to re-backup if you find that restore doesn't work since it was a pretty major bug. However, since taper-5.1.1 was only released a day before 5.1.2 (which fixed the bug) was released, hopefully, not too many people are affected.
From taper-5.0 to taper-5.1.3, there was another not so serious bug. This caused the file counts on the archives to be incorrect in certain, obscure situations. You will know if you have this bug because you will find that you have funny files on your restore screen, and some files and directories will be missing altogether. There is no way to correct the errors on the archive other than re-backing up, however 5.1.4 (and later) have a `fudge factor' which will allow to your to use your archives normally. Just run mkinfo on your archive and taper will recognize the buggy archive and fudge your info file automatically for you.
I don't believe it - the bug crept back into 5.1.5 - it's like a virus that won't go away! Anyway, 5.2 corrects it.
In versions 5.6 to 6.1 (inclusive), there was an obscure backup bug which causes a problem if there were two buffers queued for output when the tape drive was closed. Unfortunately, there is no fix for this, however, it is a relatively rare bug, and at most, you will lose the last two blocks of the backup. This bug only occurred if you used triple buffering.
In versions up to 6.1.3, there was a problem with internal compression of files > 32K. It was a spurious bug.