[Dbix-class] A count() after a grouping select() produces a "Duplicate column" error

[Vladimir Melnik]

Dear colleagues,

Here's a little snippet of the code:
	$resultset
	    ->search(undef, { group_by => [ qw(quantity) ] })
	    ->count;

It produces the following exception:
DBI Exception: DBD::mysql::st execute failed: Duplicate column name 'quantity' [for Statement "SELECT COUNT( * ) FROM (SELECT me.id, me.valid_from, me.valid_till, me.removed, me.provisioning_agreement_id, me.resource_piece_id, me.service_type_id, me.service_level_id, me.quantity, me.quantity FROM provisioning_obligation me GROUP BY quantity) me"] at /home/mmkeeper/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.24.0/DBIx/Class/Schema.pm line 1118.

What is the best way to avoid that?

Thanks in advance!

-- 
V.Melnik