Field names with '.' needs some sort of escaping
MongoDB doesn't allow '.' in keys within a hash. This needs to be detected and either get escaped somehow or else a sensible error get thrown.
The problem with escaping is that it makes searches more difficult, but it may be the least worst option.
Could you submit a test case?
This link suggests replacing with Unicode full-width equivalent could be OK: http://docs.mongodb.org/manual/faq/developers/#faq-dollar-sign-escaping
The issue is whether that should be a default behavior or optional. I can't imagine keys having full-width equivalents very often, so it might be a safe and useful default -- but would need to happen in queries as well. Or at least a helper function to escape keys used in queries would let users do it more easily.
I'll check with the new driver that its yours and will close in some way this issue on a further release that will force the upgrade to the 1.x driver as it was almost a year since I've released the optional support for it 👍