Wrong width of slide, if there is less slides than defined columns

I've got slider set up to 4 columns on large screen, but content is based on array of variable length. If there are 4 or more items, width of each item is OK, but when number is lower than 4, then each element takes equal part of carousel. This is especially an issue when there is 1 element with fluid photo - it gets HUGE.

Right now the only fix is to add container for each slide with css max-width set, but IMHO this is too much trouble especially when you got like 4 brakpoints, then you max-width need to be set-up for each one.

Further investigations draws me to conclusion that this is an issue of how flex-basis is count. Currently it looks that number of items (not number of columns) is used.