When using ClientConnectionPoolDataSource and connection pooling, a new connection / transaction is created for every new logical connection, and the resources are not freed / cleaned up in the server. They are not even cleaned up when the physical connection (ClientPooledConnection) is closed.
A logical connection is obtained by invoking ClientPooledConnection.getConnection().
I have observed that if you run the repro enough times against the same server, the number of transaction in the transaction table will be reduced now and then. I believe this is garbage collection, but I have not investigated the problem enough to tell for sure what's going on.
I have also seen some locks not being freed, causing timeouts in some applications. I don't have a repro for the lock problem at this time, but it is very likely related to this issue.
Note that XA connections are handled differently on the server, and do probably not have this problem.