Hi Peter,
A little more information on this. I've noticed a different behavior on this issue based upon whether I click on a folder icon to expand, vs clicking on the "+" sign next to a folder.
Clicking on the "+" sign to expand will cause the horizontal scroll bar to appear (if the subfolders names are longer, etc). However, I've noticed if I click on the folder name/Icon instead of the "+" sign, the horizontal scroll bar does not appear. (Actually, sometimes I see it appear, then quickly disappear).
Also, If I do the above on the last (bottom) folder in the tree list, it will momentarily expand to show sub folders, then immediately collapse down.
Let me know if you would like some screen shots or portal access.
Rob Ralston