I found a sequence which hides the message from the list.
In addition this sequence corrupts UTF encoding of the text.

1. create new message
2. submit it
3. Edit this message again
4. click SAVE and then exit the editor (click Logbook name in the header or BACK in the browser)
5. message disappeared from the list!
6. by clicking NEW message I found my lost one in the drafts, but all text was corrupted.

I've made small GIF presentation on this issue (attached, open in new window), may be this helps.