To test this, I've added a RadAutoCompleteBox to a form in a new project and am using default settings. (No autocompletesource)

The problem is that under certain conditions, manually adding a new item does not work in specific locations.

I've tested and recorded each broken case from 1 to 6 items, refer to the attached image.  The "yes" and "no" represent whether or not it is possible to manually insert an item at that position.  As an example of this happening in the actual control (also pictured in the attached image), if you populate an AutoCompleteControl with three items and then try inserting an x at the beginning, pressing the semi-colon key will simply do nothing rather than adding a new item called x.

I noticed this bug in multiline mode as well, although I'm not sure whether or not the cases differ.

Thank you for your time.

Edit: Also, it seems that autoCompleteBox.Clear() does not work in the OnCollectionChanged event.  Is this intended functionality?

Hi Chris,

Thank you for writing.

I confirm that issues exist in the latest official release Q1 2012 (2012.2 608). I am glad to inform you that we have already addressed them in our internal build and you can take advantage of this fix in the upcoming service pack, which will be available by  the end of the month. I cannot give you temporary solution due to complexity of the issue.

I hope that you find this information useful.

Kind regards,
Svett
the Telerik team