There might be something wrong with folder rights, I have seen similar behaviour with the MX 6.x versions. What happens when you close the Modeler, delete your deployment directory, start the Modeler again and run "Check widgets"?
I just tested this by upgrading my project from 6.5.1. to 6.6.0.
Running / checking widgets / creating an unversioned package all work correctly.
So there seems to be something different going wrong..
would you mind submitting a ticket with your project? I've converted a few projects just now, trying to reproduce your problem but have been unable to do so. Please be sure to mention this topic in your ticket as well.
I also went from 6.5.1. I have just deleted all the widgets and added the SprintrFeedbackWidget fresh from the appstore. When I then run the widget checker it stil complains that the widget is not compatible.