Avoid users can change Short Text of Material Id in Purchase Requisitions

Hi

We have a problem with purchase requisitions.

Users create a purchase requisition. In the field material,   type the ID of the Material but then, change the description in Short Text, for example Material 1000 is a Bearing, and the user can change this description for  Nut for example, causing problems and confusion in the following steps.

We want that if the user use Material ID can´t change the Short Text

Thank You  very much

Sergio