core-bundle/src/Resources/contao/classes/FrontendUser.php
public function findBy($strColumn, $varValue)
	{
		if (parent::findBy($strColumn, $varValue) === false)
		{
			return false;
		}

		$this->arrGroups = $this->groups;

		return true;
	}
public function findBy($strColumn, $varValue)
	{
		if (parent::findBy($strColumn, $varValue) === false)
		{
			return false;
		}

		$this->arrGroups = $this->groups;

		return true;
	}
Save the original group membership

@param string $strColumn
@param mixed  $varValue

@return boolean