Steps to reproduce:
- Edit in NWE with syntaxhighlighting enabled.
- Copy a word with a soft hyphen in it, I used "Kindergartenstudie" from https://de.wikipedia.org/w/index.php?title=Sebastian_Kurz&diff=prev&oldid=167161199.
- Insert it.
Note that CodeMirror shows red dots for the SHYs, which increases the length of the displayed syntax, while these characters are invisible in the actual text. The same might apply for other such characters as well.