Sounds to me like you log into an account set to either:

• Remember last editor, which was VE (?)
• Always use VE

And then load https://www.mediawiki.org/w/index.php?title=Wikibugs&action=edit&section=3
And get VE with only the section open, which doesn't work as you'd expect right now.

Change 282821 had a related patch set uploaded (by Alex Monk):
Check wpSection before converting textbox contents for use in VE

https://gerrit.wikimedia.org/r/282821

Yes, my preference is set to "Always use VE".

I'm not quite sure why the server sends you via the wikitext editor for this yet, but the automatic switch takes place without noticing the value of wpSection.

Change 282822 had a related patch set uploaded (by Jforrester):
Check wpSection before converting textbox contents for use in VE

https://gerrit.wikimedia.org/r/282822

Change 282821 merged by jenkins-bot:
Check wpSection before converting textbox contents for use in VE

https://gerrit.wikimedia.org/r/282821

Change 282822 merged by jenkins-bot:
Check wpSection before converting textbox contents for use in VE

https://gerrit.wikimedia.org/r/282822