Thank you for the explanation, but we're still not very sure of your exact scenario. Do you use Panel item for the "container item" that has the other 4 textboxes? If this is the case, why don't you set the borders to it instead of the inner textboxes?
If still having problems, please zip and attach your report to a support ticket and we would get back to you with more info once we review it.
the Telerik team
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