Why do my proximity mines sometimes prematurely detonate?

You shouldn't be able to place proximity mines so close to each other. Normally when you try to place a mine next to another one, the older mine will detonate. However, I've noticed glitchy behavior with these things. Sometimes a random mine somewhere else will detonate when you place a mine, and sometimes a mine will not detonate even when an enemy is next to it.

After taking a peek at the Coalesced.bin file for the proximity mines entry, I see the line:

maxactivemines = 3

I guess if you have more than 3 mines then it'll detonate the oldest mine, but due to multiplayer graphic glitches sometimes you'll still see the mine there but it won't trigger anymore.