I have a RadComboBox that is loading items on demand from a Page method. About 1% of the time, it would lose the selected value on post back. After much digging, I found that in all of those1% cases, there was a \r and/or \n character in the data stringbeing used for the item's text. Once I filtered out the \r and \n characters everything works fine.
I thought I would post this in case anyone else has a similar problem.
I would also urge Telerik to either fix this issue or to put something very clear in the documentation about this.