First off thanks a lot for this app. I use it almost in every site :).
Now onto the issue, I'm not sure if this is a bug or expected behavior due to import mechanism. Basically when a function from the api is imported anywhere from a cms_plugins.py file the plugin residing in said file fails to register, and thus doesn't show in the admin.
To reproduce this just import
from cms.api import create_page, create_title, add_plugin
at the top of any custom plugin in cms_plugins.py
this is probably a circular import problem. try importing it in the function you actually use it and not at the top of the file.