Query with left join and group clause returns only one row, even though there are multiple results

under certain circumstances, Doctrine will only return one result out of a bunch of results, for example:

$ symfony doctrine:dql "from Tafel t, t.Reservering r where t.restaurant_id=4 select date(t.tijd), count(t.id) tafels, count(r.id) reserveringen group by date(t.tijd)"
>> doctrine executing dql query
DQL: from Tafel t, t.Reservering r where t.restaurant_id=4 select date(t.tijd), count(t.id) tafels, count(r.id) reserveringen group by date(t.tijd)
found 2 results
-
date: '2010-11-14'
tafels: '1'
reserveringen: '1'

Expected outcome:
found 2 results
-
date: '2010-11-14'
tafels: '1'
reserveringen: '1'
-
date: '2010-11-16'
tafels: '1'
reserveringen: '0'

The query works fine without the left join:
$ symfony doctrine:dql "from Tafel t where t.restaurant_id=4 select date(t.tijd), count(t.id) tafels group by date(t.tijd)"
>> doctrine executing dql query
DQL: from Tafel t where t.restaurant_id=4 select date(t.tijd), count(t.id) tafels, group by date(t.tijd)
found 2 results
-
date: '2010-11-14'
tafels: '1'
-
date: '2010-11-16'
tafels: '1'