I used the tool to resolve an edit conflict at Bob the Builder This munged the formatting by replacing < and > with ampersand codes. As these symbols are widely used on the English Wikipedia, this is unacceptable and so I'm no longer using the beta.
Topic on Help talk:Paragraph-based Edit Conflict Interface
I just ran into this myself. See [https://en.wikipedia.org/w/index.php?title=Michael_Peterson_(criminal)&diff=950237197&oldid=950237182]. I had reverted the edit from an IP [https://en.wikipedia.org/w/index.php?title=Michael_Peterson_(criminal)&diff=950237182&oldid=950231864], got the edit conflict, chose my revision and accepted and then see the lead messed up. The history showed a second edit from me that appears to have come from the edit conflict resolution. Something's not right.
Interestingly, I got an EC on a subsequent article, clicked preview and saw the same formatting issues. Clicked cancel, and in the history, my original edit was there. This is just odd.
The same happened also here:
The replacement occurred for all unchanged text and all text modified by the other user (which I have accepted in conflict resolution). Those lines I did change have not been affected by the bugous replacements.
It happens not only with "<" and ">" but also with &; the commonly used "&nspb;" became "&npsb;" See https://it.wikipedia.org/w/index.php?title=2MASS_J10475385%2B2124234&diff=prev&oldid=112097269
As someone noted below, this doesn't seem to happen if I press Enter when submitting the edit, only when I click on the save button.
We had this on a recent death page <,>," and & were affected. Because of the rate of editing I ended up fixing one character type at a time, which is not ideal. Because "Recent event" articles are more likely to create conflicts, this bug is more likely to express in these circumstances.
Is there a Phab for this?
Yes. I founf this Phab: https://phabricator.wikimedia.org/T107679
That's an old task, and the issue looks somewhat different. The task for the current issue is phab:T249986
I'm able to reproduce the behavior and can confirm this is clearly a bug. I appears like the actual bug was introduced more than 3 years ago, but only surfaced now because of other changes. I'm really sorry this happened during the Easter holidays. We will backport a fix as soon as we can.
The issue was fixed and this fix is life on all Wikis. Thanks a lot for the report. --For the Technical Wishes Team: Max Klemm (WMDE) (talk) 09:28, 14 April 2020 (UTC)