The problem appears to be that the deserialisation code expects an hex-string encoding a binary array. It fails because the value it receives is not a hex-encoding of an array, but an EWKT string.

Either postgis allows EWKT strings as serialisation, which is news to me, or something else is converting the values behind the covers, maybe some type extensions in the postgis.jar.

I've posted a question on the Postgis mailing list about this. In the meantime, could you remove the postgis.jar from you classpath and try again?