My favorite recorded bass mistake is made by the Byrds' Chris Hillman on "Spanish Harlem Incident" on the "Mr. Tambourine Man" LP. On the third verse, Chris hits a wrote that is so far flat that it sounds like his string lost tension and is flopping against the pickup. Apparently this has been pointed out to Chris, who laughed and said it's proof that he actually played bass on the track because studio bass players never would have made that mistake. I imagine that the bass and drums were on one track and that they didn't feel like re-recording because the rest of the track is OK and since it was an album track, it wasn't likely to be played on radio in those days. It may have been fixed since, but it wasn't fixed on the non-remastered CD I have.