Doctrine_Query::parseFunctionExpression() produces unexpected results if the expression contains a function

When Doctrine_Query::parseFunctionExpression() is called with the following parameter and $this->_conn->expression is of type Doctrine_Expression_MySql:

$expr = "DATE_FORMAT(datefield,'%Y-%m-%d'),someotherfield"

The expected result from Doctrine_Query::parseFunctionExpressoin() would be

DATE_FORMAT(l.datefield,'%Y-%m-%d'),l.someotherfield

However, the actual result is

DATE_FORMAT(l.datefield,'%Y-%m-%d'),someotherfiel

Note the missing leading "l." and the last character ("d") on "someotherfield".
Obviously this leads to fatal errors.

This example is a result of calling addGroupby("DATE_FORMAT(datefield,'%Y-%m-%d'),someotherfield") on a Doctrine_Query object.