When importing a simple file with 5 unique rows in it into a new container using mongoimport (I will give examples below into a new container). The import tool says all went well, but only the first row is is saved. I was able to produce this behavior for TSV, CSV and JSON files.
Staring up the mongodb amazon instance from the amazon market place and upgrading to mongodb 2.2.2 via yum would be the surest way to duplicate what I was seeing. To be specific I was using the public Amazon Instance ID: ami-62da7c0b as a starting point.