This behavior is by design. We implemented it after we received a lot of feature requests to allow -0 as a valid value of the control, since in many scenarios the users first enter the '-' sign and then start typing a number. Also, there are scenarios when you tab back in a MaskedInput
with negative value, and you may need to enter - 0.12, so entering -0 in this scenario is also an expected behavior. Basically you can change the sign of a value in the MaskedNumeric
by hitting the '-' sign.
Also the minus sign can be removed along with the value of the control, on clearing the content through the ClearButton
the Telerik team