When firing the Mk6 mortar on the highest charge and the lowest elevation, the weapon can flip and fall over, due to either too high recoil or improperly configured physics for the launcher.
The problem seems to happen less frequently when the mortar is being fired less than ~90 degrees off from the initial direction (as seen in video 3).
Place a Mk6 Mortar. Press F twice to change to the highest charge, then hold Page Down until the tube reaches its lowest possible elevation. Turn the mortar 90-180 degrees to the side. Fire the mortar and observe the entire weapon including the player flip over backwards.
Video 1: https://www.youtube.com/watch?v=kY2GbG5aX60
Video 2: https://www.youtube.com/watch?v=WbxnE9EqAN4
Video 3: https://www.youtube.com/watch?v=Sly0LGfTQoU
This bug occurs in Stable, Dev, and Marksmen DLC RC.