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kotlinlang

This is not a bug. It's just that kotlin is a different language from java.

The bug is not in kotlin which has its rights to do anything like this, but Java libraries which use reflection introspections of a class sometimes do not expect this to be possible and ending with a bug. This is what happened in Jackson which ends up without either the property or the private getter.

Maybe it is not a bug but it is a flaw of the language.