After a deep research, I figured out that the issue was in the SelectedIndexChanged event logic. I am using "Indirect Subscription" approach to handle it within my Page logic, for more info please take a look Indirect Subscription Approach
Originally I was reloading controls inside the handler but it was not required since I am doing it in the Page_Load method as well, so all I need to do is to update control inside my PlaceHolder controls list. I hope it is clear, if not, please ask, and I will provide more description.