Recently, a friend of mine experienced the same problem while we were fishing the surf near San Francisco. He was using a 10' Tica rod, popular American brand spinning reel (to remain nameless), 20 lb. test monofilament line, 50 lb. test shock leader, 4 oz. sinker and soft plastic baits. We had been fishing for about a half hour (lots of casts) when his bail accidently closed upon release of a cast. He then inspected his equipment and couldn't find any problems. He blamed the incident on operator error. He continued fishing. A few minutes later, the bail accidently closed again! He inspected his equipment again and couldn't find anything wrong. On subsequent casts, the bail failed again, so we called it a day. He called a few days later and said he found a problem using a magnifying glass. The bail arm had a hairline crack that was invisible to the naked eye. He replaced the bail arm and return spring and hasn't had a problem since. I wouldn't say he found the cause of the bail accidently closing, but close inspection of a reel using a magnifying glass may be good place to start. Just trying to help.