strange compiler bug

[Paul de Bra]

When compiling metafont on a 386, using the AT&T (development system 4.1.6)
c-compiler, I get bogus errors like this:

"mf2.c", line 1811: illegal character: 043 (octal)
"mf2.c", line 1811: cannot recover from earlier errors: goodbye!

"mf4.c", line 1362: illegal character: 043 (octal)
"mf4.c", line 1362: cannot recover from earlier errors: goodbye!

The commands for compiling each file look like:
cc -O -I.. -c mf2.c

I compiled the stuff with gcc without getting any errors.
Also, when I say

cc -P -I.. mf2.c; cc -O -I.. -c mf2.i

I get no errors, so just by splitting the compilation in 2 supposedly
equivalent parts the errors go away.

Has anyone seen this before?
(Please don't tell me I should use gcc instead. I want to try the X11 stuff
and the gnu utils, using gas and gnu-ld, don't like the shared libraries.)

Paul.
(debra at research.att.com)