Sometimes, and I wasn't able to deterministically reproduce the problem, when you try to create a record, Thread.current[:mongoid_batch_insert] is erroneously set and never executed and therefore the records never gets persisted...

By the way, is there any good reason why you are using a local thread variable, which is basically a global variable, for controlling this stuff?

I was trying to isolate the problem and fix it but I couldn't get the specs suite to run without failing so I didn't feel confident of going and making changes to the codebase.