Dropdown changing the selected index

Question

Hi, I have added the autopostback="true" and as you can see when you select a county, after selecting California as the state, that the posback sets the county back to --Select--

Why is it doing this? How do I make it hold the county I selected? I have an idea about it, and I have also added OnSelectedIndexChanged="DropDowncounty_SelectedIndexChanged" to the dropdown and a sub in the code behind. How do I make this work?

 I have attached the vb.net page here.

 

See this page at http://localhost:64250/Jumbo-mortgagerates.com/jumbo_loan_limits.aspx

To see it live. Once you select California, the counties will load and then select property type and click the button. The Counties dropdown will reset to the --Select-- option.  Why is this happening?  The First dropdown is working fine...