I had exactly the same problem as Duncan at the end of November, not once but twice. Both times, the edit was very soon after the initial submission. The first time, I realised I had attached the wrong file so hit “Edit” to see if I could change it but that simply caused the initial post to disappear. Having re-typed the reply and submitted it I then wanted to add some text so tried another edit but got the same result – a vanished post. Luckily, having been alerted to the problem the first time round, I had taken a copy of the text this time so could start again.
*** Tried an edit again. Seemed OK this time!
*** What “spam filter”, by the way?