I have not noticed this prior to 10.2
It does not happen every time (one of those bugs!) but there are times when the triangle on the table of contents does not respond when clicked and so does not show the next level down of the contents.
I have only noticed this on User Tools with the table of contents open and it seems to happen after updating the tool then going to another point in the contents.
It is corrected by closing and opening the table of contents.
There does not seem to be an obvious set of tasks I do before it happens but seems to involve one of the following flows:
Go to a specific point in the user tool
Edit at that point
Copy a paragraph
Close the edit window of the tool
Move to another part of the table of contents and click the arrow
A similar flow also seems to do this but involves copying from word then switching to Accordance.
I'm afraid this does not happen every time