Thank you for your quick reply.
Prior to posting this issue yesterday, I had already read a Telerik document concerning the use of EnableLoadOnDemand property and the ItemsRequested event with regards to RadCombos and server-side access. I had applied the info in that document, but it was not resolving this issue. So I removed all of those changes that I made to my page, including the removal of the EnableLoadOnDemand property. After some frustrations, I then posted this issue.
When I reviewed what you had posted, I found that your example was almost exactly like mine, with one difference. You had
populateRadCombobox inside of an if (!IsPostBack) statement, and I did not. If you place your call to
populateRadCombobox outside of the if (!IsPostBack), you will find that this also causes CheckedItems.Count property to always return a zero.
In the past, I’ve used if (!IsPostBack) in the Page_Load event more times than I care to admit; it was an oversight in this case. So even without the use of EnableLoadOnDemand, you can repro this problem if you place
populateRadCombobox outside of the if (!IsPostBack).
I wonder though; shouldn’t the postback have caused all the items that had a checkmark to become unchecked during the postback? That’s what was driving me crazy; everything I had checked was still checked after I clicked my button, yet the CheckedItems.Count would return a zero.