In the new-nav, searching for
[tag1] [tag2] defaults to [tag1] or [tag2].
I use “or” tag search maybe once a month, and it's inconsistent with the rest of the search syntax — if I search for
[tag1] is:q foo, I get results that are questions containing “foo” and having the tag [tag1].
There's a way to switch to an “and” search: click on the little “all” button next to the “any” button. But that's cumbersome. The most useful feature should be the default.
[tag1] [tag2] search for [tag1] AND [tag2], like it does in the old nav.