[css3-multicol] column-span in overflow

What is supposed to happen when "column-span:all" element is encountered in overflow (specifically in the case where additional columns are added outside of the overflowing box)? What should it span?

We can say that if a "column-span:all" element does not fit in the original box it should be treated as "column-span:1". Reasonable?

There will be a boundary case of course, where "column-span:all" creates overflow, and "column-span:1" fits without overflow. I am not sure what to do in that case. I am thinking it should force balancing preceding content anyway, and then get pushed into overflow (and only span one column there).