itallic code span not rendered properly

[Aerilius]

I'd like to report a small issue with the markdown engine:

under_score is rendered improperly without code span (Firefox 25.0/Ubuntu),

under_score works,

under_score fails as well

Examples for implementations where it works:

• https://github.com/jbt/markdown-editor
• http://markable.in
• https://stackedit.io