Hello cudafunk,
Thanks for contacting us!
Here is the situation as I understand it. The ‘Buy it now’ is the registration button for each event.

Before a filter is selected, it brings you to the cart just as expected.

After filtering though, the register button does not properly work

For me though, it works just fine and everything is added the cart as expected.

I’m using Chrome 34 on Mac OS X 9.2. Are you on a different browser or system? Or where you able to fix this already?
Let me know if I’m understanding this incorrectly.
Cheers!
– Casey Driscoll