Stage.setX(), setY() not working properly

I have attached a JavaFX application. In it I create multiple undecorated windows. When I take one window very close to another they must stick to each other. When sticking to left or right they must be at the same height. But setY is not working properly. The window gets sticked at a different Y co-ordinate.
Also initially I am using setX to set the X coordinates of the windows initially . It is also not working properly.
Please have a look