Update cautious constraint to bump the tethered element back in to the scrollable area if it oversteps the left edge of its scroll parent.
Update cautious constraint to avoid scenarios where a tether is unnecessarily flipped horizontally and creates a horizontal scrollbar.

This could be construed as a fix to the 'together' constraint itself, but for the moment I'm relegating it to the cautious constraint.
Update cautious constraint to prevent flipping when target and element are both left-aligned and the left edge is scrolled off the page.

In these circumstances, the user is likely scrolling to the right either to see the full element or to see something else on the page. Flipping the element could cause the contents to move in to an unscrollable region.
Update cautious constraint to ensure the element flips when it would otherwise disappear off the left edge of the scroll parent.
Update cautious constraint to refrain from flipping a top-edge attachment.

There are not many cases in which this configuration would not be scrollable, since the document typically grows in height. There might be oddities in some scrollParent + overflow:hidden scenarios, but I hazard they would be no less odd than they were before...