To reproduce:
- Create a GridViewMaskBoxColumn with standard mask type and mask set to "aaaaaaaaaa".
- Bind the grid to the following DataTable:
private static DataTable GridDataTable()
{ 
    DataRow dr = default(DataRow);
    DataTable dt = new DataTable();
    dt.Columns.Add("Description");
    
    dr = dt.NewRow();
    dr[0] = "1234567890";
    dt.Rows.Add(dr);
    
    dr = dt.NewRow();
    dr[0] = "abc";
    dt.Rows.Add(dr);
    
    return dt;
}

- Click the first cell in order to enter in edit mode.
- Click the second cell and you will notice that the text is wrong.

Workaround:
- change the value in the CellEditor intialized event handler:

void radGridView1_CellEditorInitialized(object sender, GridViewCellEventArgs e)
{
    if (e.ActiveEditor is RadMaskedEditBoxEditor)
    {
        RadMaskedEditBoxEditor editor = e.ActiveEditor as RadMaskedEditBoxEditor;
        editor.MaskTextBox.Value = "___________";
        editor.MaskTextBox.Value = (string)radGridView1.CurrentCell.Value;
   
    }
}

IIF function in Expression for calculated columns does not work.

On DateTime column when IsNull or IsNotNull option has been chosen it throws exception.

When changing parent form Localization property the column's header text does not changes appropriately

When adding a new row in underling data source and SelectLastAddedRow is true the newly added row is set as current but it is out of visible grid area.

CellFormatting should not me thrown for filter cell elements.

Column's FormatString property should be applied to filter cells as well.

Excel-like filtering throws an exception if there is a combo-box column, which contains values of types System.DBNull

Assigning a custom type convertor to the column's DateTypeConvertor property does not work as expected.

When exporting to excel through ExportToExcelML class, Guid type values are not exported.

When applying a filter to RadGridView, there is inconsistency between underlying data source current row and grid's current row.

In some particular cases it is possible to experience a undesired scroll behaviour in RadGridView with lots rows. When clicking on first or second grid's row, it scrolls on row down and the first row goes out of sight.

If in underling datasource there are more than one field, which do not allow null values, trying to set them in DefaultValueNeeded event leads to exception "Column [columnName] does not allow nulls"

RadGridView remains in edit mode if the focus has been taken from RadToolStrip's item (for example: ButtonElement is clicked)
It is an issue in the obsolete RadToolStrip. Works as expected with RadCommandBar.

If there is an underling font in the grid, exported file cannot be opened from MS Excel.

If there is conditional formatting it takes wrong settings for base cell colour.

In some cases Columns Group View has impropriate cells layout, mostly rendering two borders on one and the same side for some particular cells.

When loading layout in RadGridView, combo box columns lose their data-sources.

There is a weird behaviour when the row is in edit mode and the user clicks consecutively in a different ComboBoxColumn. The drop-down pop-up is shown bun immediately disappear if the previous cell was also from ComboBoxColumn.

When update certain record of underling DataTable, the RadGridView makes this record as CurrentRow. This leads to unwanted scroll and select of this row.
Comment: Set the SelectLastAddedRow property of the GridViewTemplate to false.