Repro steps:
1. Create a new VFX and add it to the scene
2. Open Project Settings - VFX
3. Change the Fixed Time Step value to something large (1)
4. Reset it back to the default 0.01666667
5. Observe the particle speed.

Expected outcome:
- The current fixed time step value to apply

Notes:
- Possibly related to the recent work with time and update modes
- Setting Fixed Time Step to larger values sometimes throws 'Thread group size must be above zero' errors.
- Found on trunk/master