Scrolling down broken with "perf top --hierarchy"

[Markus Trippelsdorf]

Scrolling down is broken when using "perf top --hierarchy".
When it starts up everything is OK and one can scroll up and down to all
entries. But as further and further new entries get added to the list,
scrolling down is blocked (at the position of the last entry that was
shown directly after startup).

-- 
Markus