HELP - windows disappear completely when minimized

[Richard Owlett <rowlett@cloud85.net>]

ENVIRONMENT:
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.

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?
TIA