NA %*% 0 == 0 (PR#4582)

R-1.8.0: Does not happen for me on WindowsNT4.0 either (self compiled 
binary, gcc-3.3.1).

Does for me (RedHat, R 1.8.0 and 1.7.0).

I guess the problem is compiler-dependend, because I get that "0" in a 
self-compiled R-1.7.1 (has been compiled with gcc-3.2.?).

Is your binary self-compiled or from CRAN (Duncan Murdoch compiled the 
CRAN binary with gcc-3.3.1 as well, AFAIK)?

I get it in Win XP with both 1.8.0 (compiled with 3.3.1) and 1.7.1
(compiled with 3.2.x).  I'd guess one of two things:

 - it depends on the runtime library.  (Windows versions use MSVCRT,
but the exact version used depends on the system you're running on.)
This doesn't seem to explain what happens on Linux, does it? 

 - it depends on some uninitialized variable.  do_matprod is
surprisingly complicated, so I can't tell if this is what's happening.
For some reason Insight won't debug that function properly.

Duncan Murdoch