Repo steps:
1. Plug a particle position into a 'Rectangular to Spherical' node
2. Plug the output from 1 into a 'Spherical to Rectangular' node
3. Set the new position value back to the particle position
4. Observe that the particle is no longer where it was.

Expected outcome: the two nodes to negate each-other.

Note:
- Looks like Rectangular to Spherical is outputting theta and phi in radians, but Spherical to Rectangular is trying to convert degrees to radians:
return new[] { VFXOperatorUtility.SphericalToRectangular(VFXOperatorUtility.DegToRad(inputExpression[0]), VFXOperatorUtility.DegToRad(inputExpression[1]), inputExpression[2]) };

Probably removing the two VFXOperatorUtility.DegToRad operators will resolve this.