Which modal implementation are you using? Bootstrap or Bootbox?
If it is from Bootstrap, can you try to add the following:
The above should help prevent dismissing the modal when the background is clicked as a workaround. It should still be dismissible by pressing Esc key.
As for the SUBNM dropdown itself, can you please contact your local Cubewise office to help you submit a ticket on this? We will have a look and do further assessment on the above. Thanks!