Confusing but probably logic behaviour...

I am playing around with a C++ project using DirectX. Mostly out of curiosity and just the plain fun of learning things. At the moment its a large grid (a plane basically) and a player controlled box that I controll with a gamepad. It can run and jump. There are no real performance issues even though the grid is about 30 000 vertices and no culling is done. Yet. 

I am using the DX::StepTimer for delta time between frames and it seems robust. 

However. I noticed a HUGE difference in DT between frames when the application is …