rod grid sizing problem with hflex=min & span

Steps to Reproduce

1) run grid-span.zul
2) resize the window
3) scroll down to trigger ROD

Current Result

1a) the columns don't span the grid width
1b) there's an unnecessary margin on the right of the grid
2) the grid and columns snap into the expected position
3) the columns shrink again (sometimes one can see the width flickering - depends on browser speed)

Expected Result

consistent sizing as after step 2)

Debug Info

reproduced with FL 8.6.1.FL.20190212
potential side effect of a previous fix in 8.6.1 ( 1a) didn't happen in 8.6.0.1, 1b) happens in 8.6.0.1 too)

Workaround