what happen if we use external clock to which doesn't support hardware timing?

Hi all,

  I have a card PCI6023E, which does not support hardware timing. I have an external clock of frequency 5kHz to PFI0. In the MAX, I setup a task for generating pulses sequence of frequency 1kHz to counter 0, ask shown in the following figure

In next tab, I set the external clock to PFI0.

And then I run it, I saw in the scope that it will generate a pulse train of 50Hz. I just wonder why it doesn't show error because PCI6023E won't support external clock. Also, why it generate 50Hz pulse train (even I change the external clock to other frequency, it still generate 50Hz pulses).