In the diffs normal spaces have been replaced by non-breakable spaces.

As the first edit also removed some empty lines this reminds me a bit of T152671. I wasn't able to reproduce the issue in Firefox in similar circumstances. Which browser are you using?

I have the newest Firefox.

In the first edit, I actually used the tool http://dispenser.homenet.org/~dispenser/cgi-bin/webchecklinks.py?page=fi:Jarkko_Nieminen
but I then copied the whole page without saving and changed to NWE and pasted the content there and then saved the changes.

In the second edit, I only changed order of text (https://meta.wikimedia.org/w/index.php?title=Steward_requests/Permissions&diff=prev&oldid=16197726) and fixed a few parameters, and NWE made some unneeded changes that broke the template.

In T152671 "All empty lines have been removed." In my examples, not.

I now can reproduce:

1. Copy some text with 2 or more consecutive spaces (either from the VE surface itself or from somewhere else, e.g. your text editor). Actually, just 2 spaces are enough to reproduce the bug.
2. Insert them in VE (both reproducible in visual and source mode, also both with Ctrl-V and Ctrl-Shift-V).

Expected result: The spaces are inserted as spaces (i.e. as U+0020).
Actual result (at least in Firefox): The spaces are inserted as NBSPs.

I could reproduce it with Chromium as well, it’s apparently not limited to Firefox!

Change 336939 had a related patch set uploaded (by Esanders):
Replace non-breaking spaces when pasting into source

https://gerrit.wikimedia.org/r/336939

Change 336939 merged by jenkins-bot:
Replace non-breaking spaces when pasting into source

https://gerrit.wikimedia.org/r/336939

Change 337417 had a related patch set uploaded (by Jforrester):
Update VE core submodule to master (2f38291c4)

https://gerrit.wikimedia.org/r/337417

Change 337417 merged by jenkins-bot:
Update VE core submodule to master (2f38291c4)

https://gerrit.wikimedia.org/r/337417