why the slice cursor move back to the center?

[pingdan]

my steps:

1. at the upper right view, move the red cursor line from center to right.
   2.at he upper left view, I change the slice along z axis through mousewheel backward or forward. but the red line automatic move to center.
   I think when I change slice along z axis, the other axis should keep last status.

I use GetOrigin() to get the vtkPlaneSource origin point. the data is right.
defaut figure

step 1, move the red line

step 2, change the slice with mousewheel

[pingdan]

I have found the reason.