Interestingly enough, there may be some factual basis in that statement.
I have noticed that the individual RJ-48 jacks for the BRI's are covered
with a metal or metallized plastic hood, and the HD jack is the only one that
is simply there...with no cover or shroud over the jack.
Personally, I don't think it makes a damn bit of difference considering the
nature of an ISDN circuit and the path taken by the data internel to the
BRI card, but it's easy to see how such a conclusion could be drawn simply
by looking at the obvious difference in the jacks.
If you consider the adverse conditions ISDN overcomes enroute to your
MPOE (normal copper, cross connect boxes, type-66 blocks, etc.) once it's
plugged in to the PortMaster, a particular type of jack shouldn't affect
performance, unless there is an obvious manufacturing defect involving the
jack's installation on the PC board.
Damien