Posts don’t have titles, topics do.
The button shows posts’ raw content.
Nonetheless, why would you need to see a topic’s title in a post’s raw content display?
You click on the raw button in the topic view, so you already know the topic title, which is always visible at the top of the screen.
The title of a topic does not really relate to the content of a post. Therefore, it doesn’t really belong in a popup showing the ‘raw’ post content. It also doesn’t contain any raw content to display.
So I’m not sure how useful it would be to show this information. 