Hi Pawan,
I am not sure of what be might be causing this strange behavior without a working sample. I have tested this issue in the attached sample with Essentail studio V.4.x. I was not able to reproduce the issue. Is it possible for you to upload us a minimal sample or modify the attached sample to reproduce the issue here? This will help us to analyse the issue further.
Sample :
GDBGComboBox.zipBest regards,
Haneef