It is really too long to post it. A google search reports that the same problem happens in other packages when reimplementing the __getattr__ function.
I will try to reproduce it with a shorter code. The funny thing is that it depends on the length of the stack of the function calls: it shows up when the stack has length one, it doesn't when it's zero or two. The code works the same anyway, it's only that the message it quite annoying.
Yeah, it looks like something additional needs to be done in the smach UserData class to prevent this from happening. I'll look into it, don't worry about a minimal example.
Thanks for bringing this up!
-j