Dependent drop down with value node is is invisible on screen

Hi All,

   I have a case to design 2 drop downs.

  1st is normal drop down based upon the z table

  2nd is drop down based upon the value selected on the 1st drop down. My drop downs are perfectly visible even i can select but the issue is once any event has triggered on the screen the value of the drop down is vanishing and the value is going to be first value of the drop down.

  Please guide me the check points to make it possible and it is a value node too.

Thanks,

Shyam K Gangisetti