Entityform multipage modal window shifts location on "next"

I've got a multipage entityform that opens in a modal window according to the modal module instructions in the first answer here:

http://drupal.stackexchange.com/questions/108945/how-to-use-entity-form-...

Everything works fine at first, but when I click next, the modal window suddenly drops below the fold, so that only the top is showing on the screen, and the second page auto-positions at the bottom of the form.

Is there a module that can help me reconfigure or redesign this issue, or does it have to be coded?

Drupal 7.x
Entityforms v. 7.x-2.0-rc1
Modal Module v. 7.x-1.x-dev
Modal Forms v. 7.x-1.2