BUG #4438: regexpression gives the error by working with [

The following bug has been logged online:

Bug reference:      4438
Logged by:          Anatoli Lau
Email address:      ailau@sharematrix.com
PostgreSQL version: 8.3.3, 8.3.4
Operating system:   Linux Suse 10.3
Description:        regexpression gives the error by working with [
Details:

select regexp_matches('/a/b[534]', E'(.*)\[([0-9]*)\]');
always gives the error but
select regexp_matches('/a/b{534}', E'(.*)\{([0-9]*)\}');
works good, the problems comes up only when '[' used