Routing Rules dropdown field allows editing

I noticed that when I had defined a routing rule and went to apply to my repository when I clicked into the field to select it, it didn't open the dropdown for choices (like blobstore) but instead simply showed the cursor next to "None" (default text).
You could then type in other text (which was checked against for validity on exit).
The behavior didn't seem necessary unless I'm missing something. Could be an improvement or wontfix but caused me extra time and is inconsistent so am filing.

See attached vid.