You used a dev version of a tool that is not meant to be ran in production or for any serious task and then complained it didn't work with your attempt. As this bug is not present in the real prod version of mongodb, it doesn't make sense to criticize mongodb for it. Also next time RTFM before using a tool you don't know much about.

I feel this is a justifiable defense, if you use a pre-release version of anything you should recognize that you are taking a risk.

The 32-bit stable versions have the same behaviour, and the MongoDB guys on IRC did admit that data corruption is not a very elegant way to handle it.