When hitting the down directional key within the  navigation tree at 
the moment you select the first child (if the node is expanded) or the 
next sibling, but you stop when you reach the last sibling. I do not see 
any reason for that. After reaching the last sibling the next parent 
sibling should be selected. So that you only stop when you reach the 
last root-item or one of its visible descendents. A workaround is to go back to
the parent and down again.

Reproducible: Always
Steps to Reproduce: