`ObjectReader.readValue(JsonNode)` does not work correctly with polymorphic types, value to update

[basmastr]

There seems to be a difference in behavior of ObjectReader::readValue(JsonNode) and ObjectReader::readValue(String). In particular I've found a difference in how they treat the combination of @JsonUnwrapped and @JsonSubTypes and a custom deserializer. I am attaching two minimal test cases. They are identical but one uses ObjectReader::readValue(JsonNode) (and fails) and the other one uses ObjectReader::readValue(String) and passes.
Tested on version 2.9.2.

unwrappedSubtypesBug.zip

[cowtowncoder]

I hope to have time to look into this. One thing to keep in mind is that Tree Model is meant to be exact representation of the content, without transformations, and is explicitly different than POJOs.
So more like "untyped" structure of Lists and Maps, for which unwrapping is not applied (unwrapping requires existence of properties, concept that is POJO-specific, not applicable to Maps or ObjcetNodes).
Similarly polymorphic handling isn't really applicable either, with minor exceptions (like POJO property declared as Object should be able to handle JsonNode values if polymorphic handling is enabled).

[cowtowncoder]

Ok. This is interesting... usage seems correct. And using jsonNode.traverse(mapper) instead of jsonNode works. So something does seem wrong here.

[cowtowncoder]

Ok. So the problem is not so much use of String or JsonNode in itself, but rather how JsonNode is traversed: it is passed ObjectCodec, which in this case is ObjectReader.
That is fine in itself but reader is configured with object to update, which causes problems.
I'll need to see if there is a way to easily clear "object to update" for this particular use.

[cowtowncoder]

Fixed for 2.9.3 (and was actually already working for `master, 3.0.0-SNAPSHOT).