JDBC6.5-1.2 other possible problems

How/when does the JDBC actually release a postgres connection? I ask
because, when I try running stuff under native threads on Linux, unless
I explicitly close a connection it's left open after the Connection
object itself has gone out of scope - it's visible as a "postgres" task
in the task display, and isn't recovered until the JVM itself has been
killed. Also, it seems that if too many of them occur I get another
major error and the postgres back-end dies.

Platform (sorry, didn't mention in other post):

SuSE Linux 6.0 kernels 2.0.36 and 2.2.9, SMP and not, Blackdown Java
1.2, LiveSoftware's JRunPro servlet engine, Postgres 6.5. This problem
seems to manifest when running under native threads, which is not
*officially* working yet, but seems to.

Is the Postgres JDBC driver thread safe?

--
Rachel