RouterOS v5rc1

I’m having troubles with L2TP/IPSec on win7

I can connect just fine the first time and after that the connection fails.
I’ve discovered that if I flush the installed SAs I can connect again so the trouble seams to be similar to this http://forum.mikrotik.com/t/finally-l2tp-ipsec-is-compatible-with-windows-or-almost/18381/1 and both seam related to this http://support.microsoft.com/kb/942429/en-us

I’ve tried with version 4.11 and 5rc1 and I have the same problem on both.

Iphone and Mac OS X 10.6 work fine

Is there any workaround for this?

Thanks