The following bug has been logged on the website:
Bug reference: 6457
Logged by: Albert Cieszkowski
Email address: albert.cieszkowski@cc.com.pl
PostgreSQL version: 9.0.6
Operating system: CentOS 5.x
Description:=20=20=20=20=20=20=20=20
OS, base and client encoding UTF-8:
peimp=3D> select '=C5=9Awinouj=C5=9Bcie' ~* '\m=C5=9Awinouj=C5=9Bcie\M';
?column?
----------
f
(1 row)
peimp=3D> select '=C5=9Awinouj=C5=9Bcie' ~* '\A=C5=9Awinouj=C5=9Bcie\Z';
?column?
----------
t
(1 row)
but:
peimp=3D> select 'Mr=C3=B3z' ~* '\mmr=C3=B3Z\M';
?column?
----------
t
(1 row)
peimp=3D> select 'Mr=C3=B3z' ~* '\Amr=C3=B3Z\Z';
?column?
----------
t
(1 row)
I believe it is connected with bug #5766 and #3433.