This documents the limitation discussed in https://github.com/twbs/bootstrap/issues/12126:
> When using column reordering and using the affix-plugin on an element positioned with push, the affix plugin doesn't work correctly - the element affected by the affix plugin is positioned to the left even when the element is in a column positioned on the right.
Seems to affect Safari (tested in version 8) only.
That issue has (unfortunately) been closed, so this at least documents the behavior.