Well, it looks like I've found something.
In JComments.init from jcomments-v2.1.js there's a check if the host name is still the same in the url as in location.hostname. This check doesn't count for port numbers in the hostname.
I've written a simple check to filter out the port.
original line 275 in jcomments-v2.1.jsvar h=location.hostname,d,i1,i2;i1=r.indexOf('://');if(i1!=-1){i2=r.indexOf('/',i1+3);if(i2!=-1){d=r.substring(i1+3,i2);if(d!=h){r=r.replace(d,h);}}}this.requestURI=r;var th=this;jtajax.startLoading=function(){th.busy.show();};jtajax.finishLoading=function(){th.busy.hide();};},
my testi2 = d.indexOf(':');if (i2 !== -1){d = d.substring(0, i2);}
I've inserted it just before replacing the hostname with the original one. This gives me the new line.
new linevar h=location.hostname,d,i1,i2;i1=r.indexOf('://');if(i1!=-1){i2=r.indexOf('/',i1+3);if(i2!=-1){d=r.substring(i1+3,i2);if(d!=h){i2 = d.indexOf(':');if (i2 !== -1){d = d.substring(0, i2);}r=r.replace(d,h);}}}this.requestURI=r;var th=this;jtajax.startLoading=function(){th.busy.show();};jtajax.finishLoading=function(){th.busy.hide();};},
So at least my comments now are send to the server

Wo.