If you lay 2 mines within splash range of each other, then shoot one (or have someone fly by and trigger it) the explosion for the first mine will set off the second one in the typical minefield chain-reaction.

If you lay one mine, then someone else lays another within splash range of the first. Neither mine's explosion will trigger the other one.

Likewise for rocket splash damage.

Pants-on-head stuff right there

This smells like one of those things where a dev will pop up in a week or so and explain that it's not a bug, just a design decision to reduce load on the server when people make big minefields, and then we'll be all, "Well, that's lame, change it please!"

so lets cut through all that and jump right to the fix it or die part!

Yeah, the one explosion should trigger the other player's mine.