This seems like a bug to me...but maybe it's not. More below.
I'm working on a new JSON-LD hinting CodeMirror add-on (which I hope to contribute here once it's "ready). However, I've hit a weird bug.
Using this demo, pressing @ or Ctrl+Space within a key opens the auto-complete for the reserved JSON-LD keywords. However, if you use Ctrl+Space in Firefox or Edge an space is inserted...but not in Chrome...strangely.
The code is about 40 lines of effective code:
It's possible it's my code (this is my first such thing and it's based off of reading lots of hinter variations--both core and community written). That said, it only breaks in FF and Edge (in my tests)...so...maybe it's a bug in CodeMirror?