Here is a screen shot of the behaviour. This happens every 3 to 5 minutes when using the editor including after a preview pane has been opened.
This behaviour only started about two days ago and I suspect it may have coincided with the new(?) draft auto save feature on the post editor (that's the first time I noticed the feature anyway). It happens whether I'm quoting another post or not.
This must be only when replying to existing threads - it hasn't happened composing and previewing this OP. I also cannot see the draft saving feature at the base of this editor.
Any suggestions? Can you investigate and if possible rectify at your end? I can attach the report file that Safari generates if that will help.