Ahh, that makes sense. I found this document from hpe.com with the 3com product end of sale.
Looks like 3C589D-TP was on 7-Jan-1999 and 3CCE589ET was on 5-Feb-2004. Could be 3com changed the way buffers etc. was working in the latter/later model.
Not that it helps any of us much, but it's always good to gain more knowledge