Notional Load as per AISC 360-05

i have a symmetric structure with symmetric loads..

how does staad generate notional loads?

i used the notional load feature in staad.pro v8i release 20.07.05.15, the generated loads are not symmetric.. why?

below is the input file i used..

STAAD SPACE
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
       1 0 5 0
       2 0 5 4
       3 4 5 4
       4 4 5 0
       5 0 0 0
       6 0 0 4
       7 4 0 4
       8 4 0 0
       9 0 7 0
      10 0 7 4
      11 4 7 4
      12 4 7 0
      13 0 7 2
      14 2 7 4
      15 4 7 2
      16 2 7 0
MEMBER INCIDENCES
       1         1         2
       2         2         3
       3         3         4
       4         4         1
       5         5         1
       6         1         9
       7         6         2
       8         2        10
       9         8         4
      10         4        12
      11         7         3
      12         3        11
      13         9        13
      14        10        14
      15        11        15
      16        12        16
      17        13        10
      18        14        11
      19        15        12
      20        16         9
      21         1        13
      22         2        13
      23         2        14
      24         3        14
      25         4        15
      26         3        15
      27         4        16
      28         1        16
DEFINE MATERIAL START
ISOTROPIC STEEL
E 2.05e+008
POISSON 0.3
DENSITY 76.8195
ALPHA 1.2e-005
DAMP 0.03
END DEFINE MATERIAL
MEMBER PROPERTY AUSTRALIAN
1 TO 4 13 TO 20 TABLE ST UB150X14.0
5 TO 12 TABLE ST UC100X14.8
21 TO 28 TABLE ST A75X75X5
CONSTANTS
MATERIAL STEEL ALL
MEMBER TRUSS
21 TO 28
MEMBER RELEASE
1 TO 4 13 TO 16 START MY MZ
1 TO 4 17 TO 20 END MY MZ
SUPPORTS
5 TO 8 FIXED BUT MX MZ
LOAD 1 LOADTYPE Dead  TITLE LOAD CASE 1
JOINT LOAD
13 TO 16 FY -1
LOAD 2 NOTIONAL X
NOTIONAL LOAD
1 X 0.002
LOAD 3 NOTIONAL Z
NOTIONAL LOAD
1 Z 0.002
PERFORM ANALYSIS
FINISH

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