I have recently discovered a small bug in Google Analytics that prevents an event from being collected in the reporting if the event "label" is a number.
The situation I encountered this issue in was when using my Google Analytics Wrapper to track custom events. I had the 3rd label argument as the funnel step number that the visitor was currently on, it was simply an integer (1, 2, 3...) and after some waiting time I realised that Google Analytics was not accepting these events.
After testing I simply added a "step" prefix to the value, making it a string ("step-1") and the events immediately began recording as expected.
This may be a bug but may in fact be a method that Google uses to prevent a developer from tracking specific users, which is against the terms of service, where Google assume that an integer is a user ID or similar.
If anyone else has run into this issue and has any further insight, it would be great to hear.