why would Linode port number make a difference to Arduino?

We have been running a custom server on our Linode at port 8000 for over a year now. Most of the users access this server with client software running on a Windows, Mac or Linux OS. We haven't experienced any problems.

Recently we began a project to port this protocol to a deeply embedded Arduino device. The Arduino is the client; our Linode hosts the server. However we are noticing very frequent timeouts from the Arduino while it tries connect to port 8000. We have run an extensive matrix of experiments including knocking down Apache and running our server on port 80. Arduino connects perfectly with port 80. Best we can tell the actual port number is the variable which determines whether or not the Arduino can reliably connect to the Linode.

While the source of this "problem" may well reside in the Arduino library, I thought I would ask this forum if any one can think of a reason why Linode port 80 and port 8000 would be different. ie. are their subtle timing differences which might be spooking the Arduino library to go down a timeout branch?

Thanks in advance for your help.

bob