> It turns out that it's also a good behavior in the sense that you can
> get the other two behaviors (ignore all invisible text properties and
> obey all invisible text properties) in the following way:
> 
>    (let ((buffer-invisibility-spec nil)) (current-column))

It's not just neat, it's splendid.  We can dispense with that
rear-nonstickyness and DTRT with plain rear-sticky, invisible
text.  Stephen, please try with the attached patch, it should
work out of the box.