Q: User picture disappears after shutdown

Has anyone noticed a missing User Picture after Shutdown?

I've had the same one for well over a year and then last week I noticed on start up at the User screen the picture was missing.

I went into  system preferences > users/groups > and pulled down the drp down menu besides the picture square and chose a small avatar

picture to use. All seemed good. Shut the Mac down and then restarted again and it had gone again. Tried another picture and same thing.

Always had a picture from my library and not an Apple system one.

I am the Admin and I have no guest user set up.

It's a trival thing and I tend to shut down when travelling at the end of the week but has anyone had the same issue and solved it?

As below; MacBook Pro using Lion 10.7.4

As always many thanks in advance.