Hrm.. I suspect there's something subtle going on, because get_NSString works in many other places.
If you're not getting a valid UTF8 value, it could be due to UTF8 encoding issues - are you using Python 2 or Python 3?
How exactly is it failing? Is it a munged string, or a hard crash? If it's a crash, then the issue could be in reference counting - if the string is being released too early.
Can you narrow down the problem case to something simple? In particular, can you reduce the problem to something really simple that can be added as a test case in Rubicon?
(Also - just so you know: I'm based in Western Australia, which is UTC+8 - I'm not ignoring you on IRC, or waiting a long time to reply to messages :-)
Russ %-)