Wrong fontification of bold and italic text in the presence of punctuations

On commit 74c0a06 

Whenever a punctuation symbol follows the delimiters of bold font and an italic section is present afterwards, the rendering in between is slightly off. For a change in order (first italic, then bold) the problem does not occur.

```
**Fat**, normal *italic*, normal **fat**
```

This is probably related to issue #223 . In addition, it does **not** occur in `gfm-mode` 