Since the early 2000's, the District of Delaware local rules have prohibited talking to a witness about the subject matter of their deposition testimony during a deposition:
RULE 30.6. Depositions Upon Oral Examination.
From the commencement until the conclusion of deposition questioning by an opposing party, including any recesses or continuances, counsel for the deponent shall not consult or confer with the deponent regarding the substance of the testimony already given or anticipated to be given, except for the purpose of conferring on whether to assert a privilege against testifying or on how to comply with a court order.
It's not uncommon for visiting counsel defending depositions in Delaware cases to not know this rule. …