It seems however that the problem comes from the unusual CSS style selector that you use to set the width of the RadTextBox controls. Based on the information of this help article, you should correct your CSS rule like this:

Copy Code
.three_column .RadInput
{
   width: 448px !important;
}

Note the missing .riTextBox class from the selector. You should not apply width for the inner input element (which this selector controls), but only to the outer wrapping span element controlled by the .RadInput class. After applying this change on my side, the problem didn't reproduce any more.

Yet another approach to fix the issue is to use the inline Width property. However, based on your code I suspect that you intent to change the width by CSS rules and that is why I would recommend the modification in the code block above.