I'm sure it is a bug, though the navigation you're talking about is slowly becoming obsolete because [there's a new navigation being tested currently](http://meta.stackexchange.com/questions/259220/new-navigation-alpha-2-released), and it's already in the second alpha.

This new navigation doesn't have this bug: when you select all the bountied questions, it says:

>Questions that need answers

And when you select specific tag(s), the tag name is just prepended to the title:

>'javascript' questions that need answers