horiz. line after columns

any idea how I could correct the following?

after the columns, many themes don’t show the horizontal line (<hr>) at all,
some show one of ±1cm, some just for the width of the column above and
some just show it for the whole page-width (which is what I mostly) need.

Where should I look for changing this behaviour?

thanks 🙂

http://ww.wp.xz.cn/extend/plugins/columnizer/