So far, cannot reproduce it either.

Another diff, another example (confirmed this happens in Safari): https://fr.wikipedia.org/w/index.php?title=Ludmila_Pagliero&diff=next&oldid=109908395

<s>An example on en.wp: https://en.wikipedia.org/w/index.php?title=Titin&curid=1668482&diff=637694922&oldid=637694521</s>
EDIT: I'm removing this example which is actually related to a different bug.

I've made a video : https://www.youtube.com/watch?v=A8rlUExGPnI&feature=youtu.be MAC OS-X 10.10 Safari 8.0.2

Thanks for the video!

If a page has something like the following
{{Cochise County, Arizona}}
{{Arizona}}

[[Category:Unincorporated communities in Cochise County, Arizona]]
[[Category:Unincorporated communities in Arizona]]

In VE It's possible to type in the area of Category placement which sort of "override" Categories feature - look at the attached screenshots.

Note: the Categories have not actually disappeared though - diff made it look like it.

This might be the same problem as T85671.

Change 194194 had a related patch set uploaded (by Catrope):
Work around Array.prototype.splice being broken in Safari

https://gerrit.wikimedia.org/r/194194

Change 194194 merged by jenkins-bot:
Work around Array.prototype.splice being broken in Safari

https://gerrit.wikimedia.org/r/194194