Checker reporting an ERROR affects EFFECTIVELY_FINAL symbol flag in subsequent source files

[XN137]

I was upgrading error-prone to 2.31.0 on a branch for a project and it started reporting both DefaultCharset and FormatStringAnnotation violations in a module.
The former were expected and valid but the latter left me scratching my head as the FormatStringAnnotation checker was not modified between the versions afaict.

I tried reproducing the FormatStringAnnotation violations in an error-prone unit test but the code was passing the check just fine.

Then I tried to reproduce the whole scenario in an error-prone integration test and was successful, so I have pushed the test code here:
XN137#1

note:

• it looks like after an ERROR has been reported by UnusedVariable, the symbol flags are different in subsequent files and the EFFECTIVELY_FINAL flag is no longer set and so FormatStringAnnotation is reporting "phantom violations"
• the symbol flags stay the same when UnusedVariable is set to WARN
• the symbol flags stay the same when the file comes before the file that contains the UnusedVariable ERROR violation
• in the IT I have replaced DefaultCharset with UnusedVariable to show its not related to DefaultLocale / String.format having any shared state with FormatStringAnnotation

please take a look and let me know whether this is expected behavior in errorprone (or javac) or a potential bug?
If the former, maybe this should be documented somewhere as it can be really confusing if checker B starts reporting "unjustified" violations just because checker A has already reported an ERROR.
sorry in case i missed something obvious that would explain this behavior.