This seems to be caused by DocViewer Parameter.
It appears in the tree with a "+" next to it, as if it is a folder rather than a leaf node. Clicking on the "+" briefly reveals a sub-level with the label "_hideName", and then the tree resets, as described above.
Searching for "doc" also causes this behavior, since the search display tries to show the _hideName subnode. Search for "docu" doesn't have this problem, because
If you then repeat either the clicks or the "doc" search a second time, the "_hideName" subnode shows up and the tree stays open.
See also Bug #2382, which has morphed into a the same thing as this. I'm requesting that this bug be retained for this specific issue, and Bug #2382 be re-diverted to address it's original purpose, which is a different issue from this one.