I spotted the bug at nlwiki and tried the inputbox before and after the fix. It's fine now, regardless of a title is entered or not.
You can try it at any of the pages on this list.

I encounter an issue that may be related: insertion of unnecessary bdi tags (bidirectional isolate element). To reproduce it:

1. Use the Chrome browser to select any line of a history page in any name space using Dutch for interface language (I didn't test other languages)
2. Paste it into a reply to any comment
3. When prompted accept conversion to wikitext
4. In either visual or source mode 2 bdi tag pairs appear

The same when copying a watchlist line, except that 3 bdi pairs appear
This search returns 187 examples: https://nl.wikipedia.org/w/index.php?search=insource%3A%22BDI%22&title=Speciaal%3AZoeken&profile=advanced&fulltext=1&ns1=1&ns3=1&ns5=1&ns11=1&ns13=1&ns15=1&ns101=1

According to the OSM answers my problem is not related, nor is the rendering of the N31 aqueduct (in the same map) as a bridge related. All these bugs may be about wrong rendering of styles however.

Hi, I encountered an error that may be related, see the map in nl:Koningsbrug (Harlingen): the Celsiushaven (to the east) is too wide due to the yacht wharf being treated as water. Per OSM the tag waterway=boatyard is handled incorrectly, see Dutch Wikipedia Helpdesk and Dutch OSM community.