i found out that i can blow away locked chests with stuff in it (tested in singleplayer, don't want to test it on a public server with chests from other players, tested with newest mt-version from git) with TNT
normal chests, full normal chests and full locked chests are blowable too.
i don't know if this is possible on public servers with chests from other chest. if yes it should changed.
also full chests (even not locked) should not be destroyable with TNT.