After installing version 6.4 the submit button for Bookings went having the text “SEND YOUR BOOKING” to “Undefined”. The text is being replaced in the file bookingsform.js in the function em_booking_form_update_booking_intent
Looks like the variable EM.bookings.submit_button.text.free is undefined.
I fixed this by commenting out the lines that were setting button.value to EM.bookings.submit_button.text.free