Hi Mz91184,
I tried to replicate your issue as described above. When I set the new field to null and return to edit, it is still null. This was a known issue with 2.1.2 and below. It was fixed with 2.1.3.
It seems like the upgrade to 2.1.3 didn’t take. Did you commit it to the SVN or did you just try a clean install to test with first?
Do you have a version of 2.1.3 with no third party add-ons of any kind? If so can you try your three steps again in a clean install?
If you do not have a clean install, you can disable extensions to perform the test.
It is possible that SVN’s caching is interfering with this as well. It wouldn’t hurt to clear that cache.
The “Save Revision” button issue is a known bug we are working on 😊
Please let us know how it goes.