MalformedJsonException thrown when reading manually edited JSON data in Postgres

Encountered this exception while modifying JSON data in the DB:
org.apache.cayenne.value.json.MalformedJsonException: Unexpected end of document

The data in question is simple test JSON like this:

{"test": "some value"} 

Same exact data that is inserted via java code is totally fine.
I suspect that it could be Windows related, but need to check.