messages in the inbox disappear for an instant and then all come rolling back

I have just had a few problems with accessing my gmail in Thunderbird even though it was all working perfectly this morning as always. Managed to get it sorted and had to close down and then re-open Thunderbird. Now, when I click on a message to read it and then close it, something odd hapens - it's as if all the messages in the inbox disappear for an instant and then all come rolling back in. Not quite sure how to describe it but hope you get what I mean. I've never seen anything like it before. Help!!