You have the following scenario.
The UpdateValueEvent property is set to "LostFocus" and set no mask ( Mask= "").

When the input box is focused, press the minus sign key. You can see the that the minus is showing as expected. 

Then press a number and the "-" (minus) disappear. By pressing number key again the minus appears again.

A workaround: 
Setting the UpdateValueEvent property to PropertyChanged


Available in R2 2016 SP

In MaskedTextInput the ClearButton will make the Value "" but it should make it NULL. All other InputControls have null value after pressing ClearButton.

No-masked TextInput works fine - the ClearButton makes the Value Null.

As a workaround, you can use the ClearCommand, bind it to Command from your ViewModel and the execute handler can set the bound Value to null.

Mask="" (no-mask) and FormatStyring =n3 or n4 , n5.

Value is 0.

Typing 0 then ".", then 0, then 0, then 5 produces 0.5000 but it should produce 0.0050.

Fix available in LIB Version 2016.1.404.

MaskedNumericInput with Mask = #6.3. When there is no digit grouping (you can turn it off from  the region / format settings in windows, no digit grouping means no symbol for grouping) the control produces Exception on load.

Part of the Value or the whole value is selected in no-masked NumericInput.

Pasting a copied text is not successful. For example 4 is the value and 4 is selected. Pasting "123" produces "1" but it should produce "123".

I think it would be great to have a IsMultilineAllowed property for this control, as AcceptsReturn property is only designed to ignore the return key entered by the user.

Here is my post in the forum:
http://www.telerik.com/forums/paste-multi-line-text-when-acceptsreturn-set-to-false
========
Reason for Decline: The desired request is custom logic that could be implemented by inheriting the RadMaskedInput control and overriding HandlePaste.

Mask is "a-a". Value is set to "M-M".

The MaskedTextInput control must internally coerce the Value to "MM".
Instead , MaskedTextInput'Value is "M-" which is wrong.

Other example of the same issue:
Bound Value is bbaabbaabbdd, Mask is "aa-aa-aa-aa-aa-aa"
The result is - value becomes bbbbbbddaaaa.

Workaround:
Use custom Mask Token (check help article: http://docs.telerik.com/devtools/wpf/controls/radmaskedinput/how-to/howto-create-custom-token.html)

 public class CustomToken : ITokenValidationRule
    {
        public bool IsRequired
        {
            get { return false; }
        }

        public bool IsValid(char ch)
        {
            return ValidChars.Contains(ch.ToString());
        }

        public char Token
        {
            get { return '$'; }
        }

        public TokenTypes Type
        {
            get { return TokenTypes.AlphaNumeric; }
        }

        private string myValidChars = "0123456789qwertyuioplkjhgfdsazxcvbnm";
        public string ValidChars
        {
            get { return myValidChars; }
        }
    }

    TokenLocator.AddCustomValidationRule(new CustomToken());
            InitializeComponent();

   <telerik:RadMaskedTextInput Mask="$-$"  

RadGridView with CellEditTemplate with RadMaskedDateTimeInput.

Select a GridViewRow. Press ALT  + N Key (or other key with letter/digit).

Argument Exception occurs in MaskedDateTimeGridViewEditor.



The issue is reproducible in Q3 2015 SP (1104) version of Telerik UI for WPF.
The fix will be available in Q1 2016 Release.

Pasting text in TextInput with No-Mans and UpdateValueEvent=LostFocus is not successful.

This operation clears the whole Value.

 <telerik:RadMaskedTextInput Mask="" UpdateValueEvent="LostFocus"/>

Available in LIB version: 2014.3.1305

The Mask property of the RadMaskedDateTimeInput cannot be set or changed via binding. Internally it is always set to "d".

Fix available in LIB Version 2017.3.1009.

For example: 

RadMaskedCurrencyInput with Culture="da-DK" and VALUE 12345.67 and Mask=#9.2. In this culture the currency symbol is "kr."

In WIndows 8, the NumberFormat.CurrencyPositivePattern is 2 (meaning '$ n').

In Windows 10, this pattern is 3 (n $). 

So in WIn8, WIn7 or WIn10 but if you change the pattern programmatically to 2. Th result is:



Actual: "kr.___.___._kr,12" this is what we see on load and on focus in control. Editing does not change the value.

Desired: 'kr. ___._12.345,67' in pattern 2

Control also produces ugly results with pattern 0 and 1. Control seems to work ok with pattern 3:

Actual and Desired: '___._12.345,67 kr.'

* this could be achieved on Win 8 with change setting or out of the box in Win10.

==============

Workaround (if applicable and desired formatting in the specific scenario)

Set in code behind:

InitializeComponent();

CultureInfo info = new CultureInfo("da-DK");
 info.NumberFormat.CurrencyPositivePattern = 3;
            
 this.maskInput.Culture = info;

Available in LIB version: 2016.3.1010

This is reproducible in a NoMask scenario.

The method should be called after the text that should be copied to the clipboard is extracted. In its original implementation it should only set the text to the clipboard. You should be able to override it and replace the text or use different method for copying into the clipboard.

For example:
public class CustomMaskedInputControl : RadMaskedDateTimeInput
{
    protected override void SaveTextToClipboard(string text)
    {
        Clipboard.SetDataObject(text);
    }
}

It would be really useful to be able to specify a maximum number of significant figures for Telerik RadMaskedNumericInput as this was requested by a client.