Hi Claire,
I'm assuming that the web form isn't a Marketo embedded form, which means you can't track it that way...
At first thought it may be something to do with Munchkin itself - perhaps it's not actually working in that environment for some reason, and therefore not recording those events. You may need to get your developer to take a look at the JavaScript on the page to see if there are any errors occuring.
Let us know how you go with that.
Regards,
Brody