Thank you for your post.
I haven't been able to replicate the issue you're having so I have a few of questions.
1. Can you replicate this over and over as well as in different models or does it just happen?
2. Does anything come up in the Ruby Console (go to 'Window > Ruby Console' and recreate the steps)?
3. What was the exact process you took to get this issue to occur?
Also, would you be able to send the model across to firstname.lastname@example.org
so that I can have a look at it? This might help shed some light on the issue.