Hi All,
I've spent far too long staring at this problem and searching for a fix, I'm finally giving up and posting here for help!
I've created a simple Northwind based application using WebIDE on my trial HCP account. It works great as both a standalone app and embedded into a Fiori launchpad within my HCP Portal on the same trial account. It deploys to my HCP account no problem and runs from there fine.
This is how it looks when run standalone:
I'm sure many of you will have seen this app before 
This afternoon I've added the <appname>.spec.xml file to enable it to be created as a widget in HCP Portal, then used the Content tab in HCP Portal to add it as a new widget. This has all appeared to have worked correctly, however when I then publish and test my Portal site, I see the following:-
As you can see, the first entry in the master list is not selected, and I get a "Not Found" text at the top. If I click on the first entry in the master list, I then get this:
The Detail pane never loads. In Chrome's console I see the following:-
and then if I refresh the page I see the following:-
Its been a long day and no amount of me staring at this is switching any lightbulbs on for me to fix it - any ideas?!
Cheers,
G.