tpope/vim-markdown — pull request #75 by wejrowski (2014-11-17 00:04:59+00:00)
Title: Add syntax match for horizontal rules to fix highlight problems.

Currently when you add a horizontal rule via ***, it will try to highlight any following characters as italics until you close the asterisk. Quite annoying if you use HRs, or even just use asterisks to visually break content apart while editing.