Given the following code:

==== BEGIN CODE ====
template <typename A, typename B>
class SomeClass
{
};

#define MYMACRO(BLOCK) \
{                      \
  BLOCK                \
}                      \

int
main(void)
{
  MYMACRO({
    SomeClass<int,int> test;
  });
}
==== END CODE ====

gcc (3.3.5 on Debian sarge, 3.4.4 on FreeBSD 6.0 from base and 4.2.0 on FreeBSD frmo ports) fails to compile it, complaining that MYMACRO was given too many arguments. For example, with 4.2.0:

==== BEGIN COMPILER OUTPUT ====
% g++42 -v -save-temps -o macroarg macroarg.cc
Using built-in specs.
Target: i386-portbld-freebsd6.0
Configured with: ./..//gcc-4.2-20060218/configure --disable-nls --with-system-zlib --with-libiconv-prefix=/usr/loca
ib/gcc/i386-portbld-freebsd6.0/4.2.0/include/c++/ --infodir=/usr/local/info/gcc42 --disable-shared --disable-libgcj --prefix=/usr/local i386-portbld-freebsd6.0
Thread model: posix
gcc version 4.2.0 20060218 (experimental)
 /usr/local/libexec/gcc/i386-portbld-freebsd6.0/4.2.0/cc1plus -E -quiet -v macroarg.cc -mtune=i386 -fpch-preprocess -o macroarg.ii
ignoring nonexistent directory "/usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/gcc/i386-portbld-freebsd6.0/4.2.0/../../../../i386-portbld-freebsd6.0/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/include/c++/
 /usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/include/c++//i386-portbld-freebsd6.0
 /usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/include/c++//backward
 /usr/local/include
 /usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/gcc/i386-portbld-freebsd6.0/4.2.0/include
 /usr/include
End of search list.
macroarg.cc:16:4: error: macro "MYMACRO" passed 2 arguments, but takes just 1

==== END COMPILER OUTPUT ====

For completeness since it is asked for, following is the pre-processor file which is incomplete for obvious reasons:

=== BEGIN PRE-PROCESSOR OUTPUT ===
# 1 "macroarg.cc"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "macroarg.cc"
template <typename A, typename B>
class SomeClass
{
};






int
main(void)
{
  MYMACRO;


}
=== END PRE-PROCESSOR OUTPUT ===

It seems to be triggered when the type is parameterized on at least two types. Removing the MYMACRO({...}) wrapping makes it compile. Putting just about anything except certain template heavy stuff inside it also compiles.

(The above is obviously a contrived example to trigger the issue; my real usage is a macro for critical sections with guaranteed mutex cleanup.)