Master - Slave Specification X to slave node have different Y coordinates

Hi,

I'm running a simple structural model to understand the issue I'm facing in a bigger model with Master-slave specification in STAAD. 

I defined a master node at elevation Y1 and slave nodes at elevation Y1 and Y2.  After running the calculation the X displacements of the node  at the elevation Y1 and Y2 are completely different even it is the same at the same elevation . Also,  I'm not able to find out a possible relation within the X(Y1) and the X(Y2)

Could you please help to understand the result?

Following is the input file:

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 25-May-23
END JOB INFORMATION
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 0; 2 1 0 0; 3 0 2 0; 4 1 2 0; 5 0 3 0; 6 1 3 0;
MEMBER INCIDENCES
1 1 3; 2 3 4; 3 4 2; 4 5 6; 5 3 5; 6 4 6;
DEFINE MATERIAL START
ISOTROPIC STEEL
E 2.05e+08
POISSON 0.3
DENSITY 76.8195
ALPHA 1.2e-05
DAMP 0.03
G 7.88462e+07
TYPE STEEL
STRENGTH RY 1.5 RT 1.2
END DEFINE MATERIAL
MEMBER PROPERTY AMERICAN
1 TO 6 TABLE ST W14X873
CONSTANTS
MATERIAL STEEL ALL
SUPPORTS
1 2 FIXED
DEPENDENT FX CONTROL 3 JOINT 4 TO 6
LOAD 1 LOADTYPE None TITLE LOAD CASE 1
JOINT LOAD
3 5 FX 200
PERFORM ANALYSIS
FINISH