remember, the general way the ~supported environment matrix~ works is
client down one version.release from server
client equal to server
client ahead one version.release from server

so the 4.1 client to a 5.1 server would place the whole environment so it
falls outside the support matrix
        (ie, all bets off)
but when you took the client to 4.2, that put it back into a slot in the
~support matrix~

I don't think we could call this specific case a bug since (due to their
support matrix) that combination probably isn't tested and for sure isn't
supported.

sorry, I hated to say that... I'm sounding more like tivoli support each and
every day :-(

Dwight