[gentoo-user] gcc not downward compatible?

[Peter Wood]

Hi list,
A few days ago I upgraded gcc from 4.1.2 to 4.3.1-r1 (upgrading 
Eclipse-sdk to the latest ~x86 version made installing gcc 4.3.1-r1 
necessary, so I thought I would stick with it on my test box).
Now I am re-emerging world and have noticed that a number of packages 
which compiled fine  with the old gcc don't compile with the new version 
anymore and have to be unmasked in /etc/portage/package.keywords. QT4 is 
one of them, just to give an example.
I don't really mind using the ~x86 version of these packages, but wonder 
why the old, stable packages won't compile with a newer gcc. Isn't gcc 
supposed to be downward compatible?