BUG #10785: error if using x>n AND x<m in where clause, BETWEEN n AND m works as supposed

The following bug has been logged on the website:

Bug reference: 10785
Logged by: j.l.
Email address: lunda(at)bitmessage(dot)ch
PostgreSQL version: 9.3.4
Operating system: Linux 64bit (ubuntu 12.04)
Description:

DOES WORK:
create index planet_osm_point_city_50k_index on planet_osm_point using
gist(way) where
(((capital IS NULL) OR (capital <> 'yes'::text)) AND
(place = ANY ('{city,town}'::text[])) AND
(population IS NOT NULL) AND (population <> ''::text) AND
(regexp_replace(population, '[., ]', '')::int > 50000));

DOES WORK:
create index planet_osm_point_city_50k_index on planet_osm_point using
gist(way) where
(((capital IS NULL) OR (capital <> 'yes'::text)) AND
(place = ANY ('{city,town}'::text[])) AND
(population IS NOT NULL) AND (population <> ''::text) AND
(regexp_replace(population, '[., ]', '')::int between 50000 and 99999));

DOES NOT WORK (ERROR: invalid input syntax for integer: "tower"):
create index planet_osm_point_city_50k_index on planet_osm_point using
gist(way) where
(((capital IS NULL) OR (capital <> 'yes'::text)) AND
(place = ANY ('{city,town}'::text[])) AND
(population IS NOT NULL) AND (population <> ''::text) AND
(regexp_replace(population, '[., ]', '')::int >= 50000) AND
(regexp_replace(population, '[., ]', '')::int < 100000));