Lucky you, didn't see our network, and have to deal with the %$#!-storm when we networked our test equipment. Apparently the culprit was a bad switch, but again not my field. Maybe they just mucked up the installation of the lab switch, I don't know. I do not have significant (or really any, not for decades) experience in networking so have no doubt you are correct, just happened to hit a bad case fairly recently that was painful. My understanding was the signal shields were OK but they grounded the external shield on the cable past the isolation transformers someplace -- again, I do not know, vague memory of a couple of years ago. I am sure signal lines were STP but never quite understood the ground issue, unless there was an outer shield under the sheath? Or they tied all the grounds after the isolation transformer? I honestly don't know, just dealt with the aftermath and heard "ground cables through the switch". I strongly suspect a mistake on the installer's part.
Gotta' get back to work - Don