Problem with settings for multiple rendered item fields

Patch with fix.

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The problem here is that the property’s combined ID and the field’s identifier are, in principle, completely different things. It might often be the case that they match, but it’s not necessary, and sometimes not even possible (e.g., for datasource-specific properties). Therefore, your proposed solution is definitely too simple, since it would break the current correct behavior for lots of sites.
I also don’t quite see how it would even solve your use case: since the $combined_id of all three fields is the same, this would still return the same config for all three fields, just (potentially) a different one than before. I fear that, due to architectural restrictions, the actual information needed to pick the correct field config is unavailable at this place in the code.

For a custom highlight processor, you might be able to make this work, however, by temporarily (just in code, without saving) removing the other two fields from the index when retrieving the value of the third one. That way, the correct field’s config will always be picked.
Not very pretty, I admit, but the best I can come up with. Other suggestions very welcome, though.