I have tried this on multiple machines, running both Windows 7 and Windows 8
2.76b & 2.77
If I use the VSE Speed Control to adjust the speed of a scene it effects the angle of particle objects
Exact steps for others to reproduce the error
I've a few extras so you can see what you're doing better.
Open Blender and delete the cube
Add a plane
Move it up a little so you can see what you're doing better
and add another plane (Plane.001)
On the second plane (Plane.001), create a new particle system
In the Render panel, set the particles to appear as Objects, Set the object to Plane
Turn the size up to 0.2 so that you can see what you're doing better
Bake the particle sequence
When you play the animation, you will see that the particles are planes that are all parallel to the plane that is emitting them.
Create a new scene - myself I like to call this scene "edit"
In the new scene, go to video editing view
Go to the timeline and add the scene "Scene" to the timeline (the first scene, with the particle system of planes in it)
Add a "Time Remap" effect to the scene
Grab the right hand handle of the scene, and drag to the left to speed up the scene
Now play. Or render. You will notice that the rotation of the particles has changed. They now rotate as they fall.
This also works if the particle is set to Group rather than Object.