Tree with hflex'ed and width'ed treecols doesn't work properly

I have a tree with hflex=1 and with 4 columns with widths 50px, 70px 110px and hflex=1. They are put inside an hbox with width 300px. What I'd expect is the hflex column to take the remaining 70px (300 - 50 - 70 - 110), but it takes 300 instead.

Please see the fiddle at:

http://zkfiddle.org/sample/1pv5qaa/2-treecol-with-hflex-bug