Replace function BUG

In postgreSQL 7.3.2 when I execute the following query

select replace('test %400% result', 'result', 'ok');

it returns "test % ok"

And If I Execute:

select replace('test %%400%% result', 'result', 'ok');

it returns the correct result: "test %400% ok"

If this is a known BUG please tell me because I need to fix this.

Thanks

Nicolas Bottarini