When using the registration format, the item selection does not specify the use of AND confirm the format of a number. I have found this to cause continuing problems using your tool to collect registrations for individual sessions at an event. The result, if a user enters an 'X' or a name instead of the required number, e.g. '1', then the registration is accepted, but no session is selected. As a result, if the number of seats in a session is limited, the user is out of luck if seats run out because although the system sends them a confirmation of their registration, it does not include confirmation of a session. The code for the field should confirm the format of the data entered.
On a live event if you try to enter something other than a number the value is cleared out and reset to the default value of 0 when you click to any place outside of that box. If a customer/contact is typing in their name or placing an X then when they click the register button, or even just click a blank section of the website then that box changes back to 0. If they click the register button and that value is 0 then they are registered as if they did not purchase that item.
If you are referring to something else please let me know and I'll be happy to assist you and figure this out.