Sorry about my first reply, I wasn't thinking straight. I'm not sure what the problem is exactly, but it seems like you are having problems using multithreading with kivy?
Can the code you pasted originally be used to trigger the problem?
Anyway, this might help you, I don't know...
https://github.com/kivy/kivy/wiki/Working-with-Python-threads-inside-a-Kivy-application
Good luck :)