There is a bug with the beta release 0.1.4 of Vetala. If you drag an item to the end of the list it will disappear.
You can get it back by right clicking and refreshing.
I'm working on getting hierarchy working in the manifest item view under Code tab. Being able to click drag one code.py under another has introduced this bug. Being able to click drag one code under another is not turned on yet.
Hopefully this week I can finish this feature and polish it.