After investigating, I found that the map makes the following request to the WMS service:http://geoserver.maurerstutzinc.com/geoserver/ows?SERVICE=WMS&&SERVICE=WMS&REQUEST=GetMap&FORMAT=image/png&TRANSPARENT=TRUE&STYLES=&VERSION=1.3.0&LAYERS=Hopedale&WIDTH=1034&HEIGHT=792&CRS=EPSG:3857&BBOX=-9957582.689984469,4925551.048026699,-9952642.94703141,4929334.680926913
First, it is missing the port 8080 specification and the second thing I see is that it includes an extra "SERVICE=WMS&" in the URL at the beginning of the parameters. I altered the URL and got this the request to work in a web browser:
http://geoserver.maurerstutzinc.com:8080/geoserver/ows?&SERVICE=WMS&REQUEST=GetMap&FORMAT=image/png&TRANSPARENT=TRUE&STYLES=&VERSION=1.3.0&LAYERS=Hopedale&WIDTH=1034&HEIGHT=792&CRS=EPSG:3857&BBOX=-9957582.689984469,4925551.048026699,-9952642.94703141,4929334.680926913
I used this URL http://geoserver.maurerstutzinc.com:8080/geoserver/ows?
and it is still stripping the port number from all map requests, but uses the proper URL for a GetCapabilities request when selecting the Description option from its context menu.Seems like a bug with how the URL is used to generate getMap requests and should be logged through ESRI Support. You could try the Contact Us link, however that may not get to the correct people.