This is the second report I've seen in a couple of days. You may want to check the JBoss SourceForge site and see if anyone has logged a problem report on it and perhaps log it if there isn't an existing report.
I haven't noticed the issue because we run hsqldb in an in-line mode that doesn't enable the port. This might be a workaround for you in the meantime.
If you look at the hsqldb-ds.xml you can run with this configuration:
You can then also disable the HypersonicDatabase MBean. There is a third configuration that runs the DB totally in memory. The DS config is well commented.