Using class table inheritance:
When a proxy for a subclass-entity is registered at the unit of work and another entity, which references that entities' superclass, is added or removed, the employed entity persister gets/uses the superclasses' metadata.
If the change-set of the referenced entity contains fields only defined in the subclass, the persister will create bogus SQL because it has no column names or data types: UPDATE table SET = ? WHERE id = ?
The attached test case is stand-alone, creating an SQLite in-memory DB (sorry, I'm not familiar with your test suite).
Only the path to Doctrine must be adapted at the top of 'run_test.php'.
The file 'SubclassPropertyBugTest.php' also contains a more detailed description.