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