One marker, multiple furniture positions, z offset not played properly

[Outerspacespecies]

Using Nifscope I created one piece of furniture with one furniture marker with two furniture positions A and B. Furniture pos. A is for an npc, pos. B is for the player, with different animations for each. The actors can use the furniture separately or simultaneously. All is playing well - except for the z position. Although the furniture markers have offset values x, y, and z, only the x and y offsets are played correctly, but the z offset (the height the animation should be played) remains the same for both, although their offset is 50 units.

 

Is this a Nifscope issue, or is it generally impossible to play each furniture position animation at a different height?