core-bundle/src/Resources/contao/classes/BackendUser.php
public function save()
	{
		$filemounts = $this->filemounts;

		if (!empty($this->arrFilemountIds))
		{
			$this->arrData['filemounts'] = $this->arrFilemountIds;
		}

		parent::save();
		$this->filemounts = $filemounts;
	}
public function save()
	{
		$filemounts = $this->filemounts;

		if (!empty($this->arrFilemountIds))
		{
			$this->arrData['filemounts'] = $this->arrFilemountIds;
		}

		parent::save();
		$this->filemounts = $filemounts;
	}
Restore the original numeric file mounts (see #5083)