Door knob (lever handle) only engages in one direction
MOST door knobs I know of engage the latch in either direction. You may have something broken or installed incorrectly on yours, or someone purposely had it made to do this. In fact, it is considered a "safety issue" to not have the latch retract when pushing the lever DOWN, because if you were trying to get out of the house during a fire, you might be crawling on the floor below the smoke and having to push the lever UP to open the door may be difficult. You should fix/replace it immediately.