We are not aware of such a bug in the control, nor for reasons for such behavior.
Can you reproduce the issue with our online demos (http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx) and if so, can you post a list of steps that showcases the issue so we can investigate it?
If the demos work fine for you, I suggest the following:
- compare your setup with the demo to find the difference that causes the issue
- upgrade to the latest version (Q1 2015 SP1 at the time of writing)