There are a few questions in the hot questions and in meta that make clever use of Unicode. The titles of these questions render poorly in the iOS app. For example:
To clarify, the following things seem like bugs to me:
In the feed view, there's no icon next to the question. Which stack exchange site is it from?
The feed shows the title as escaped HTML entities (or whatever the proper term would be), whereas when you click on it, it shows missing Unicode characters.
The title shows with missing Unicode characters. This might not be a bug, and just a consequence of the font used on iOS. I'm trying to determine that now. If it is due to the font, it might be worth revisiting the font and seeing if there's one that shows more characters than the current one.
It looks like other apps on iOS have trouble rendering those characters, too. Apple's Mail message list: