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HELP - windows disappear completely when minimized

I am using Jessie (8.6.0) with MATE installed from purchased DVD set.
The problem is associated with a single user. This was verified two ways. Logged in as root, there is no problem. Created a new user and then logged in to that user, no problem.

In normal operation, for each application launched its window opens and a title appears in the lower panel. These "titles" are ordered left to right in the panel. When several are open, clicking a title brings that application to the foreground. When an application is minimized an animation of a shrinking box moves from the app to its associated title.

In this ABNORMAL situation:
When an application is opened, no title appears in the lower panel.
When it is minimized, the animated box shrinks and disappears past the right end of the lower panel.

I strongly suspect "operator error".
What did I do?
How do I recover?