M6 Slam mines detonate when placed near parked vehicles and should not per the following clipping from SLAM Wikipedia article:
"The timed-demolition mode is active when the SLAM selector switch is set to 15, 30, 45, or 60 minutes. In this mode, the magnetic sensor and the PIRS are inoperable, and the SLAM will detonate after the selected time has expired."
Rarely can I get very close to a vehicle, and place an M6 Slam less than or equale to 19 meters while prone and performing the task slowly, with no other activity within the area. One time I was able to place a M6 Slam directly behind a parked M1A1 while prone.
What is likely happening when the player places the M6 Slam mine on the ground near a parked vehicle, apparently the game has the mine in "magnetic sensor mode" until the player selects the +30 seconds timer. Hence, the M6 Slam mine detonates before a player has a chance to set the timer.
The game should probably prompt through the middle mouse action menu whether to use the timer or magnetic sensor mode.