How can this abstract method error happen?

Hi.

I'm getting an abstract method error problem with Postgres JDBC (top of
exception trace:http://pastebin.com/xsDKSdiE). There isn't a stable way to
reproduce this that I found. The driver is 9.1-902.

I don't quite understand how this can even happen. Looks like all the all
statement object are created by the connection object, and all connection
objects are created by the Driver. Driver always creates connection version
4, and that connection always creates statements version 4, so it should
always implement isClosed(). I never ever used any earlier drivers (so I
don't think there is C/P mess up, but I grepped my class path too).

Can anything else ever create a connection object, which can be of earlier
version?

Thank you.