IP/Port blocked?

I work with two different Comcast Business accounts.  At both locations I can connect my laptop directly to the cable modem and get (what appears to be) completely normal internet access. Everything seems to be normal.

Unfortunately, at one location I can open a telnet session to a particular IP address over port 5223 and at the other location I cannot. I have tried multiple systems in both locations and the connectivity is the same for every system at that location. Also, I have tried the same system in both locations, to eliminate variables, and again, the connectivity was the same at that location as for all other systems at that location.

These locations are less than 2 blocks apart in a small town so I expect they are on the same Comcast segment (but, as I am not a Comcast employee, I cannot say for sure) so it would seem that this is truely account or cable modem difference.  I've reviewed the cable modem settings and cannot find any differences in settings that would account for the difference.

Does Comcast block certain connections for specific accounts and not others for some reason?  I cannot come up with any other reason why one account would work and one wouldn't.