Subject TCP/IP 6 problem

I have a problemen since the early days of firebird and Jaybird.
I'm now using firebird 2.5, Jaybird 2.2.3 and JRE 1.7.0_55.

When TCP/IP6 is installed (windows) the communications with the database engine becomes very slow. It works but is 10 fold slower.
It does not matter if it's local or remote host.
We have our system running on independent database engines on over 200 computers, mostly on local host.

When we remove completly TCP/IP 6 the problem is fixed.

I have tried on the jvm but it does not help.