Steps to reproduce:

1. Set a Standard Mask on the RadMaskedEditBox and a space a PromptChar.
2. Type some text in the RadMaskedEditBox.
3. Press the "Home" key to move the cursor at the beginning of the RadMaskedEditBox.
4. Then press the spacebar.
5. You should see the first character gets deleted but instead of leaving a space in the first position in the RadMaskedEditBox, the second character is moved in the first position and the cursor is on the second position.

If you press the spacebar again the space is entered in the RadMaskedEditBox and the cursor potition is ok.