If you call close on a logical connection, for instance as obtained through a PooledConnection, it does not check if there is an active transaction.
The close of the logical connection is allowed, and even the close of the parent PooledConnection is allowed in the client driver. This can/will cause resources to be left on the server, and later operations might fail (typically with lock timeouts because the "closed" transaction is still holding locks).
I do not know if gc will solve this eventually, but I would say the current behavior of the client driver is wrong in any case.
There is difference in the behavior between the embedded and the client driver, and there also seems to be a bug in the embedded driver.
The analysis above is a bit sketchy, so it might be required to look into the issue a bit more...
I will attach a repro (JDBC usage should be verified as well, is it legal / as intended?)