You can use the Spreadsheet Demo on the Telerik Web site.
Select one of the numeric values in the quantity column and choose Data Validation -> List.
Write H1:H3 on the Value for validation and fill the range with values.
Now make sure you enter a number that fails validation. You receive correctly the error dialog.
Close it and Check the Data Validation Rule for that cell.
It has changed to: _matrix(H1:H3)
Now perform more failed validations (closing the dialogs).
Check again Data Validation Rule for that cell.
It has changed to more nested "_matrix" such as "_matrix(_matrix(H1:H3))"
This process of corruption continues with side effects such as: dialog opened as many times as the number of _matrix in the Data Validation Value.
Tested on IE Edge, IE 11 and Firefox 47.0.1 with same results.