Here is a quick summary:
41.112 Validity of visa. (d). Automatic extension of validity at ports of entry
....
(ii) In cases where the original nonimmigrant classification of an alien has been changed by BCIS to another nonimmigrant classification, the validity of an expired or unexpired nonimmigrant visa may be considered to be automatically extended to the date of application for readmission
Can you write "another nonimmigrant classification"?