"\r" creating problem in textbox input

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XAML

Silverlight

I've a textbox for input (numeric value) of 12 digits and on the basis of that number I add some data into datagrid. For the first time when I enter any number it works correctly, but after adding data to datagrid when I enter any new number to textbox, it only gets 11 digits. when I check it in debugging mode, I find textbox having 12 digits including "\r" at the start. I don't know from where its come and creates problem.

Any kind of help will be appreciated. Thanks

GroupedManifest grpManifest = new GroupedManifest();
grpManifest.manifestNumber = txtManifestNumber.Text; // get number from textbox
LayoutManifest.DataContext = grpManifest; // set relevant data to layout
manifestList.Add(LayoutManifest.DataContext as GroupedManifest); // add data to list
dataGridGroupedManifest.ItemsSource = null;
dataGridGroupedManifest.ItemsSource = manifestList; // set data to itemsource of datagrid

txtManifestNumber.Text = string.Empty;           // emtpy textbox
txtManifestNumber.Focus();// set focus on textbox

first time this code works excellent but for the 2nd number txtManifestNumber only takes 11 digits (e.g 12345678912) and txtManifestNumber.Text has "\r12345678912" that creates issue on adding data to datagrid