XPages: Why does my url link open the doc using the wrong xpage?

I’m using a url link in my workflow notification messages, and it looks like this:

http://domsvr.acme.com/pko.nsf/0/42D2AD829BDAD89F852577EB006575C9

The default form for the db is a Task. This particular document is an Issue. When I use the link, the document opens in the browser using the Task xpage (based on the Task form) and not the Issue xpage as it should. The Issue form is set to open the Issue xpage in the browser, and the document has a Form field = “Issue”.

Why would the link open the doc with the wrong xpage? - and, how do I fix it?