Sources? They were allowed to seize sources?
I have no personal experience with being a reporter, but all my life I had been told that a reporter's sources are confidential, and this confidentiality agreement between a reporter and a source was not expected to include the employer of the reporter.
Do you think the Washington Post knew who "deep throat" was?
Whether it be a legal line or not, this action certainly crosses an industry standard line regarding the confidentiality of sources.
Yes, if I recall history correctly, Washington Post knew. All of the work product belongs to the employer. If you were an employer you’d know this and be sensitive to this. The reporter is an employee, nothing more.