sub question

But can you be sure that there is no legitimate reason for expecting
the current behaviour?

you surely know the answer.  

Actually, I don't. I was just pointing out the generic risk of fixing 
something that isn't broken by breaking something that works. There's a 
lot of conservatism in R where things don't get rationalized for similar 
reasons. For quite a while, bug-for-bug compatibility with S-PLUS v 3.x 
was considered important to allow people to port their packages between 
systems.

O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907