problem with non-greedy regex match

I _may_ have found a problem that is affecting non-greedy regex matches.

select regexp_matches(
  $$x = foo y x = foo y $$,
  $$x\s+(.*?)y$$  ,'g');

As I read it, this should match ' = foo' twice.  Instead, it matches
"= foo y x = foo " once.  The non-greedy form (.*?) should break out
at the first 'y'.

Interestingly, this works:
select regexp_matches(
  $$x = foo y x = foo y $$,
  $$x(.*?)y$$  ,'g');

It's the same regex minus the space after 'x'.

merlin