I was able to reproduce the undesired behavior - here is the PITS item for it. For the time being, as a workaround I can suggest to clear the value manually from the mask character "-".
I updated your Telerik points for this report.
A bit off-topic, I would kindly ask you to open new threads for questions that are not related to the original topic of the current thread. This will help other user with the same questions find their answers more easily.
Thank you for your understanding. If you have further questions, do not hesitate to ask.
the Telerik team