Tree collapsing causes unexpected jumps of the current item

[dschreij]

Whenever you have multiple linked items in several tree branches, there are intermittent jumps between linked items if one of the branches in which it occurs is collapsed. For example

- sequence_1
     - item_1
- sequence_2
     - item_1

If one now has item_1 selected in sequence_2, and sequence_2 is collapsed, the current item is set to item_1 in sequence_1. This is not a problem perse, but if the linked items are quite a distance apart (for instance in branches in the beginning and end of the experiment), some disorienting jumping can occur. This behavior is intermittent and does not always happen! Possibly it only happens after renaming the linked item (and thus it is possibly related to #668)