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 currentlythere's a new navigation being tested currently, 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
