**Steps to replicate the issue** (include links if applicable):
The basics to create the problem are
* Enter the wikitext for a level three or higher header ( e.g. `===test===`) into the edit box of one of a number of Wiktionaries (including en, es, zh, and uk)
* On any line that follows the header, enter plain text ( e.g. `test`)
* The end result should be something like
```
===test===
test
```
**What happens?**:
* Text is bolded
**What should have happened instead?**:
* Text should be unformatted
**Software version** (skip for WMF-hosted wikis like Wikipedia):
**Other information** (browser name/version, screenshots, etc.):
* Using the aforementioned page ([[ https://en.wiktionary.org/w/index.php?title=User:The_Editor%27s_Apprentice/sandbox&oldid=77667743 | en:wikt:Special:Permalink/77667743 ]]) as an example, this issue occurs on FireFox version 121.0.1 (64-bit, desktop, Windows) and Chrome version 120.0.6099.225 (Official Build, 64-bit, desktop, Windows).
* @Justin-Leung has also reported the issue, so it appears to not be limited to just my computer.
* For evidence the issue does not occur on all wikis, edit [[ https://en.wikipedia.org/w/index.php?oldid=1196735688 | en:w:Special:Permalink/1196735688]] with syntax highlighting on in the WikiEditor toolbar
* A screenshot showing off the issue:
{F41696961}