Could you detail exactly what you are doing, as you should be able to see newly created instances?
Using JBoss App Server 4.2 with portal 2.6.
In the Management console I go to Portlet Definitions, select the CMSPortlet and create a new instance. The instance shows up in the Portlet Instance tab. Under Portal Objects I create a new page in the default portal. I then select page layout for that page. My newly created instance does not show up in the list of available portlets to add.
Now you should use directly the Content-type CMS (without the portlet instance).
Actually the CMS portlet shouldn't even appear in the portlet definition list, i will filter those
Thanks for the report !