Unexpected TransientPropertyValueException with enhancement as proxy

Using bytecode enhancement with lazy initialization and enhancement as proxy (allow_enhancement_as_proxy set to true), an update on 1 field of an entity, followed by reading some associations of this entity fails with:
TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing

Without enhancement as proxy, everything works as usual with a single update statement for the modified field, and subsequent select for lazy associations.

Enhancement as proxy is promising, but using it in production leads to very weird issues, that are hard to reproduce in a simple test case.
Perhaps you're already aware of that kind of issues and I guess it's not recommended to use enhancement as proxy in production (neither bytecode enhancement with lazy initialization).