I have a multistep Drupal 7 form. I'd like to show it in a Bootstrap Popup.
This form works fine on a normal page however when I put it into a Bootstrap popup it closes the popup when the first button is pressed.
I use drupal_render(drupal_get_form('MYFORMNAME_form')) to put the form into the popup body.
How can I make this multistep form work properly in the popup?
when you say bootstrap popup, do you mean a modal window (http://getbootstrap.com/javascript/#modals)? Modals in bootstrap are defined inside the body of the page and just hidden/shown as needed. If you want one to act as its own window, you need an iframe in it, because submitting the form will not trigger whatever mechanism you put in place to show the modal dialog in the first place.
Another option is to use code to re-show the modal, with the form at whatever stage it is at, with each page load (next button, etc.)
A last option is to do all of the form navigation via AJAX. Then you don't ever need to put the form inside an iframe nor include code to re-show the modal with each submission of the form, since the page never gets refreshed.
IMHO the iframe is easiest, and a decent option if you don't have any qualms about iframes. You just need to place the form in a separate page and include it inside the iframe. Some theming work will enable you to turn off the normal page chrome that will make your modal look like a miniature version of your site -- you probably don't want your header, navbar, footer, etc. inside the modal.