There are serious issues with copy and paste, both from editors on my machine and from other wiki pages. I just tried to copy and paste the title of a page on enwiki to a talk page on dewiki in order to create a wikilink back to enwiki, and it did not work. The text was correctly pasted as a heading, but it was not possible to re-format it as a simple paragraph. When I tried preview, no text was shown at all. The same in version comparison view. In fact my text was lost I could not save it and quit the editor.
When I tried to copy and paste from TextEdit two paragraphs got lost and were not included in the browser editor window.
Also, the signature on talk pages is not correct. We sign with two -- characters before the four tildes.
I'll switch the new editor off now, said enough. I'll take another look at it in a year or so.
Thanks for looking into this.
Tested with Firefox ESR 45.7 on Mac OS X 10.11.6.