I've never used bump, but what happens if I am bumping in close proximity to two other phones bumping? Anyone ever play with distance thresholds? How close do you actually have to be when you "bump" for it to make a match?
Our matching algorithms evaluate more than just location to determine if two phones are a possibly match (and highly accurate location is fairly rare). So often we are able to match the correct phones even if there are others in close proximity that are also bumping. In the event that we match >2 phones, we prompt those users to bump again and compare both datasets.
Although you can sometimes trick the algorithm into matching phones that did not physically bump by shaking them from across the room, bumping will not work reliably if you do not bump into each other.