Just FYI, this bug is still present in 1.16.1 (Apr 2, 2013, rev: REL-1_16_1).
As for whether it happens when adding columns, my experience on Windows 7 is that the tree doesn't collapse when when I add columns or do other modifications through the table's Properties dialog. Otherwise, it happens whenever I complete a change that was initiated by right-clicking on any of the nodes below the table (Columns, Constraints, etc.).
Aren