Port problem since 7

Yes, yet another ports-are-blocked-problem. Albeit a difficult one.

Problem: all my incoming ports are blocked, even if I forward them in the Fritz!Box. This worked before Win7, I didn't need it during the last year, but now I'm stumped.

Specifically: Snarl.exe, listening to port 9887, that's what I am trying to get to work.


First, here are the obvious things I tried:

• Comodo Firewall: granted full access to snarl.exe (the program in question), even made a global rule for the port in question, but no change.
• Shutting down Comodo Firewall didn't help any
• Windows Firewall: disabled for private & public
• netstat -abn tells me: snarl is listening to 9889, an svchost is listening to 9887. guess that must be so. switching to port 9889 didn't change anything, anyway
• Fritz!Box is forwarding port 9887 to my static IP. THIS WORKS, cause from the outside I get a "Connection timed out (110)" instead a "No route to host (113)"
• Accessing Snarl.exe with Putty.exe via 127.0.0.1:9887 works like a charm

So to sum it up there must be another layer that can block me from the outside. Any ideas what it might be? I can think of no other network-related programs I have installed, that might interfere here.
To repeat: this isn't just Snarl, other programs that'd need an open port fail as well. (e.g. hosting a game)
I'll be very grateful for any idea.