To reproduce:

this.radMaskedEditBox1.Mask = "n";
this.radMaskedEditBox1.MaskType = Telerik.WinControls.UI.MaskType.Numeric;
radMaskedEditBox1.Value = 1234;
radMaskedEditBox1.MaskedEditBoxElement.Culture = new CultureInfo("en-CA") { NumberFormat = { NumberDecimalDigits = 0, NumberGroupSeparator = String.Empty } };