16 is the number of concurrent kernels possible on Fermi. Obviously, the number of streams that can launch is much higher than this.
Are you checking the error code from the stream creation function? I bet it returns an error when it cannot create another stream. If it does not, then this is a bug that should be submitted to NVIDIA to fix. I don’t recall any specific number listed in the documentation, it likely depends on the amount of memory available to the driver and differs from machine to machine.