Safari 3 no good with Speedstream 4100 DSL modem

After two days of pulling out my hair and almost buying a new DSL modem, I've discovered another issue with Safari 3.

*It seems that if you try to access the Siemens SpeedStream 4100 DSL modem's GUI with Safari 3, you will not be able to enter any data, make any changes, or upload new firmware.*

When you are prompted for this modem's 10 digit access code, it says "+invalid access code+".

When you are prompted for the login/pw, it says "+invalid entries+".

After many hours of frustration, I connected this modem to a Windows PC and suddenly no more problems. Now finally suspecting a Mac browser issue, I tried FireFox 2 on the Mac and it works perfectly fine.

I used to be able to access my SS 4100 GUI just fine with the older version of Safari.

Safari 2 Mac - OK
*Safari 3 Mac - NO GOOD*
FireFox 2 Mac - OK
Explorer PC - OK

Obviously I did not exhaustively test all browsers and versions but I did confirm that the latest version of Safari 3 on BOTH OS X.4.11 and X.5.2 will cause the SpeadStream 4100 to return "invalid" errors when trying to enter in any information whatsoever including the 10 digit access code.

*Additional Details:*

The following combination was confirmed to cause this problem...

Safari 3.0.4, Tiger 10.4.11 and Leopard 10.5.2
Siemens SpeedStream 4100, firmware 1.0.0.48 and 1.0.0.53 (latest)

This is a very common modem for AT&T DSL Service.