This can be reproduced in the Telerik UI for WPF demo application, demo "MASKED INPUT | Numeric Input" -> More Masked Input Examples.
When (very!) quickly following a numeric key press with a press on the enter key, the input field clears itself, causing a discrepancy between the bound ViewModel property (that is correctly updated to the entered value) and the displayed control (which is now empty). For the end result, see the attached Screenshot.
The Tab key does not seem to cause this behavior although it causes the binding to update just like the enter button.
No matter how quickly you press the enter button after entering a value, the control should display the exact value I entered and should never just clear itself.
With best regards