unique package names has no effect in group type source

i have source definition:

# ac-main + ac-updates
[source]
type = group
name = ac
sources = ac-main ac-updates
unique package names = yes

my global setting for 'unique package names' is off.

and i expect package names from both sources are made unique, only recent one kept, but it has no effect:

$ poldek --sn ac
Loading [pndir]ac-main...
Loading [pndir]ac-updates...
18018 packages read
Removed 1 duplicate package from available set
Loading [rpmdbcache]/var/lib/rpm...
2183 packages loaded

Welcome to the poldek shell mode. Type "help" for help with commands.

poldek:/all-avail> ls apache-base*
apache-base-2.2.4-1.amd64
apache-base-2.2.9-7.amd64
2 packages
poldek:/all-avail>