It is not uncommon for opposing attorneys to exchange during discover on a case. In today’s world more and more of it is done in an electronic form. Sometimes in its native electronic form that include metadata such as the document author, dates of creation-alteration and where the document was stored.
Attorneys must be careful not to disclose confidential information outside of the permissible discovery by disclosing confidential client information in the metadata. Attorney not taking reasonable precautions to keep from disclosing confidential metadata could be subject to disciplinary action and/or an attorney malpractice claim.
While the Texas Center for Legal Ethics in Opinion 665 addressed this very question, there was not a concrete answer given as they pretty much stated it would depend on the facts.