Can you confirm you page does not have a DefaultButton set (for the form or for some Panel) and that there isn't a global handler for an event like keydown that waits for the enter key to programmatically click the button? At this point I cannot think of other reasons for this behavior.
I have just tried that and it seems to work as expected with me. I am attaching here a simple example and a screen capture with the expected behavior.
All the best,
the Telerik team
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