It is a bit of a technicality, because the government lawyers meet with the witnesses and discuss the testimony in advance. But still witnesses on the stand often do not say what is expected, and there are rules to keep them from being "coached." It only seems uneccessary when you aren't the defendant.
There is a difference between on the stand testimony and OPENING ARGUMENTS....
My experience is lawyers coach their witnesses all the time, and I've never seen a trial where what was said on the stand did not get out if it was a public trial. If Mrs. XYZ wasn't in the courtroom when someone else was on the stand, surely Mrs. XYZ's friend, uncle cousin or nephew will or can be... and word gets back to Mrs. XYZ.
The idea of preventing taint of a witness is a noble idea, but it just isn't reality.
ANd as for Coached, you are joking right? Attorney's and witnesses can spend hours if not days or weeks coaching their witnesses on how best to deliver a point, what verbage to use, what clothing to wear, how to look more sympathetic... etc etc... Yes certainly they can not say on the stand what they said in those session, but coaching of witnesses is part of reality.
Way I see it, both sides got the same information, there is no reason here for a mistrial or a dismissal... disciplinary action against the prosecuting atty perhaps, but come on.