Huh. Well I did have a moment of infinity, so I changed it back to normal just to make sure and yeah it's pretty much the same, except then it turns. I turned off my collision handler, no change. There is no collision detected until the bottom of the square touches the bottom of the ramp, and then it's trapped in there. Hitting my jump button which applies an (upwards) impulse makes it teleport down by like 10 pixels. I can control it with the arrow keys (by manually changing the speed), and in the center of the screen where the two ramps meet, it moves slower (probably only moves there because I'm forcing speed on it without checking for collisions) as it inches through the wall between the ramps.
I tried to record a video, but it failed, I guess partly due to my low-end laptop.
I tried to make a simple testcase, but then nothing worked and after the second step, my body's y coordinate became NaN and stayed there.