Rotate your objects using three keyframes, not four, not less, not more.
First Keyframe: initial rotation (time 0)
Second Keyframe: 180 degrees + initial rotation (half time)
Third Keyframe: initial rotation (end time)
You MUST use the same sign for your rotations.
Following is an example:If your object was initially rotated -58 degrees, and you wanted to rotate it a full turn over 4 seconds:
1. First frame, -58 degrees
2. Keyframe at 2 seconds: -(58 + 180) = -238 degrees
3. Last keyframe at 4 seconds: -58 degrees.
This works 100% of the time. In step 2 above I added 180 degrees onto the initial rotation, but ignored the sign - the most important step.
NOTE: Starting with Design 3D CX 6.1, you can now rotate 360 degrees very easily by using the new Rotate Script FX. The Script FX are found in the FX section of the Resource palette.