Not much more than that to add!

You may have inadvertently given yourself the permission to bypass the allowed-worlds flag.

My other players can also place them though... and they're not op (and they only have the launch permission in that one world)

Tested this and works without problems for me. For example i added this to one of my fields:

allowed-worlds: [ fubar ]

And logged into "world" and was not able to place a field.

Just tested it with your latest version and it's working now - I can't place them when non op in the real world. Many thanks!