Created by: wilsaj
{position:relative} is implicitly set on the DOM element during the switch
to affix-bottom (happens in the call to this.$element.offset()), so it
needs to be cleared when switching from affix-bottom back to affix.
Recycling a jsfiddle from another issue that also demonstrates the problem: http://jsfiddle.net/eqrvupcq/12/embedded/result/
If you scroll down to the bottom of page then scroll back up, the target element jumps to the top of the screen and no longer works.