When parsing "p mybar.foo" gdb will do a global lookup of symbol "foo".
That seems a tad clumsy.

The bug, though, is that gdb may also try to lookup "foo" as a symtab.

play$ cat foo
/* Copy this to file "foo" and compile as
   gcc -g -x c foo -o foo.x
*/

struct bar
{
  int foo;
};

struct bar mybar;

int
main ()
{
  return 0;
}
play$ gcc -g -x c foo -o foo.x
play$ build/obj64/gdb/gdb foo.x
GNU gdb (GDB) 7.2.50.20100817-cvs
[...]
Reading symbols from /home/dje/src/play/foo.x...done.
(gdb) start
Temporary breakpoint 1 at 0x40044c: file foo, line 15.
Starting program: /home/dje/src/play/foo.x

Temporary breakpoint 1, main () at foo:15
15        return 0;
(gdb) p mybar.foo
A syntax error in expression, near `foo'.
(gdb)