Case type edit not saving, broken case types - how to debug?
The commentary suggests that the history of this case-type may have allowed some weird data in.

In case one did want to dig in more, a couple debug tricks that might be interesting:


Open the case-type admin UI and edit the current URL to append ?angularDebug=1. This will cause it to display a panel with the "live" content of the CaseType and its definition. This is available in most Angular pages.
If you're experimenting on a dev/staging site, you might try unsetting the definition via SQL (UPDATE civicrm_case_type SET definition = NULL where id = ...). This is sometimes useful for forcibly revertig a definition (even if the UI is misbehaved).