Incorrect output with : in multiline paragraphs surrounded by em/strong markup

The following snippet

````
*Note: This is
not supported.*
````

generates:

````

It happens with any combination of `*` and `_`. Taking away the linebreak "fixes" the problem but with longer paragraphs this isn't a good solution. Taking away the `:` also produces the correct output so I believe that something takes this as some kind of metadata.

It seems that placing a colon (somewhere in but not at the end of) the first line of a multiline paragraph which itself is surrounded by `em`/`strong` markup produces this error.