I don't know what I did or what happened, but while I was trying to adjust the width of some panes in Layout 4 all of a sudden CTE started to scroll down through the grid as if the Autopilot was activated (it was not selected in the menu), and one by one wiped out all target segments from the editor and from the TM.
I couldn't stop it, and this behavior continued even after relaunching CTE until I decided to restart Windows.
Fortunately, I had a backup copy of both the project and the TM, but what a sweat!
This is the second time, but the first time at least the TM was not wiped out.
What may have happened?