TYPO3.Flow

a bit more on this issue: setOrderings() appends rootAlias . "proposedSessionType" 
to the orderBy-Clause. And appearently multi-dot-notation has been dropped 
shortly by doctrine:

http://www.doctrine-project.org/projects/orm/2.1/docs/whats-new/en

The only possibility I can see at the moment is detect "." in the argument, 
do a join for this table and rewrite the order by statement.

Has anyone problems with that? Should I try to prepare a patch?

Great! As there is already a method "getPropertyNameWithAlias" its extremely easy to fix this:

Just change

 1public function setOrderings(array $orderings) {
 2        $this->orderings = $orderings;
 3        $this->queryBuilder->resetDQLPart('orderBy');
 4        foreach ($this->orderings AS $propertyName => $order) {
 5            $this->queryBuilder->addOrderBy($this->queryBuilder->getRootAlias() . '.' . $propertyName, $order);
 6
 7        }
 8        return $this;
 9    }

to

1public function setOrderings(array $orderings) {
2        $this->orderings = $orderings;
3        $this->queryBuilder->resetDQLPart('orderBy');
4        foreach ($this->orderings AS $propertyName => $order) {
5            $this->queryBuilder->addOrderBy($this->getPropertyNameWithAlias($propertyName), $order);
6        }
7        return $this;
8    }

Patch set 2 of change Ib6d967ccc97ed64828bea8765edea5dd8c63aa0a has been pushed to the review server.
It is available at http://review.typo3.org/4725