Expanding last node sometimes doesn't increase scroll size

[matsbryntse]

Easy to repro in gantt docs:

1. Expand API docs
2. Expand SchedulerPro - no scrollbar update

Forum post

Using the advanced demo, collapse all tasks.
Then expand each and every node in the tree,
e.g. 1, then 1.1, then 1.2 and every child node in the tree

On expanding the last node, the scroll bar doesn't change size and you cannot scroll down to the newly opened tasks without first scrolling up.