Found two problems working with setting workflow permissions to read_only:

On Admin > Workflows > Permissions:
when you set tracker_id to "read_only" for the first tracker/status, on a project that has this tracker as the first tracker, you can't chose another tracker when creating a new issue,
when you set subject to "read-only" for the first tracker/status, you can't create a new issue with this tracker, as it it required and has no default.

Editing an issue
after you change from a status that have tracker_id set to "read-only", to another status that doesn't
before you save
when you try to change the tracker to another tracker
the page refreshes and doesn't change the tracker_id

Patches attached: