underscore with brace not rendered correctly

[fyears]

While gfm is enabled:

k = marked('a_b_c_{s}');
// my expected k : '<p>a_b_c_{s}</p>'
// real k: '<p>a<em>b_c</em>{s}</p>'

Is it a bug? Or I missed something in markdown syntax?

[notatestuser]

it's a bug. see #491

[joshbruce]

Closing as most likely covered by spec compliance. See #1106 and #1216.