This is apparently one I'd have to see. I have an SMC and a D-Link router here, and they work as I'd expect, and my ports are all invisible, except for the FTP port, which I have open for my server. Please post your report here when using the router.
GRC Port Authority Report created on UTC: 2005-09-24 at 22:55:58
Results from scan of ports: 0, 21-23, 25, 79, 80, 110, 113,
119, 135, 139, 143, 389, 443, 445,
1002, 1024-1030, 1720, 5000
0 Ports Open
1 Ports Closed
25 Ports Stealth
---------------------
26 Ports Tested
NO PORTS were found to be OPEN.
The port found to be CLOSED was: 21
Other than what is listed above, all ports are STEALTH.
TruStealth: FAILED - NOT all tested ports were STEALTH,
- NO unsolicited packets were received,
- NO Ping reply (ICMP Echo) was received.