Hi Alan,
I know this thread is a little old, but I have been having the exact same problem for a year or so now. I know exactly what you are talking about. I think I figured out that the problem has something to do with data that was imported from a Mac (if you’re on a PC, like I am). If you are using data that is native to another machine, I think that might be the origin of the problem. Let me know if that’s the case!
Unfortunately, I haven’t figured out a way to solve this issue, other than to work around it, but it does give me a little bit of peace of mind knowing somewhat where the problem is coming from.