I realized right afterwards that you would need more detail. And I tried to reproduced it and couldn't (I will try again). I am using Firefox.
To the best of my recollection:
1. I composed a "send message" draft from within a pending message
2. I decided to discard it and hit "discard"
3. I saw the flashing red banner, long enough to read "will try again in n seconds" etc.
4. I saw it again, right before exiting the page
Steps 3 and 4 happened concurrently with my brain's processing the instruction the exit the page. It was all simultaneous. By the time I was actually out of the page, it was all over. I thought immediately afterwards that if I had stayed longer, I might have seen even more banners. As it was, there were only two.
Right after sending the message here about it, I went into my test group and tried to reproduce this, but so far have been unsuccessful.
Messages are the sole opinion of the author, especially the fishy ones.