I have seen threads about missing explosives. And today I checked it by myself. I planted all 3 Boom-Boom devices and suicided. After respawning I noticed that ALL MINES DESPAWNED. Not only C4 but Tank and Proximity Mines also. C'mon! As an almost full time Engineer I agree for despawning C4 after death. I agree for movemenet triggered Tank Mines (so they can't be used for suicide runs) and the ability to disarm them. But despawning is a bit... no - it's far too much. And I wanto to belive it is a bug rather intentional change.
I've been wondering why nobody seems to have died to my mines lately, I figured it was just bad luck. Going to check this out for myself later today.