Particle Tracing (the stored trajectories have the wrong dimension)

I have a model in comsol 4.3 with a 3D and a 2D geometry.
The model calculate fluid velocities in the 2D geometry.
I added the 'Particle Tracing for fluid flow' physics to the 2D geometry but after the solution is computed I get a error message:
the stored trajectories have the wrong dimension
-Dimension: 3
-Plot: traj1 (Particle trajectories).

To be able to visualize the trajectories, I have to create a 3D Plot Group
The trajectories are plotted in 3D with the z-direction being time.

I would like to visualize the trajectories in my 2D geometry. (It works if I remove the 3D geometry but I need it to get a correct simulation of the fluid velocity).
Does anybody know how I could do that?

Thanks