I have exactly the same problem. I have the problem on Mountain Lion/MacBook Air 13".
More information: after upgrading, there is a "refresh" button beside the model and an "!" on the right side. The hovered message is "There was an error while loading the resource". At this time, there isn't a duplicated one showing. As soon as I double-clicked on the model name, the "refresh" button becomes the inverted triangle button, and a start to see duplicate of the fields. Please note that I have also seen the same field repeated 4 times at one point (hard to reproduce that one though.)
When selecting the view log, I saw a couple of framework error: Cannot set property 'className' of undefined.
Hope this gives you more information.
I noticed that right after the project has been upgraded, that duplicated model did not occur. It only occurs after I have re-open the project.
I believed that I have narrowed down the problem that may help you guys to fix the bug. If I remove all stores that use the model, the duplicated model problem disappears! I used ajax proxy and localstorage proxy in my store, and those proxies are configured in the store (and not in the model).
I'm on Mountain Lion. Also, as I mentioned, I don't see the duplicated fields until I re-open the upgraded project.
UPDATE: Just open up the same project under Windows 8 using the Windows version of Sencha Architect 2.2, and it has the same problem.
UPDATE #2: After removing all the stores, I saved the project. Re-opening the project has all models having a "refresh" icon (instead of the inverted triangle.). No duplicates yet. Now, I can also reproduce the problem with the following steps:
1. click on one of my models and expand it. Save the project (and hence updated the .architect file)
2. Close the project, and re-open the project.
3. I start to see duplicates and the one model that was expanded before is expanded.
4. Close the project.
5. Remove the .architect file
6. Open the project.
7. All models having a "refresh" icon.
8. Expand one of the models. No duplicates.