Some inputs cause tool to hang after a few hundred lines of output

I can provide a mongoexport (1GB of JSON) and the commands I can. After writing about 280 lines of output fairly quickly, it stops writing any further output, even if I leave it for a while (I was expected hundreds of thousands of lines of output, based on my input). When I kill the process, there is no error output or backtrace to help identify where the code got stuck.