After Alt-clicking an object to pick it, it seems that only Alt-clicking away from the object unpicks it. The documentation at: http://www.manifold.net/doc/mfd9/maps_guide.htm indicates that Esc or Ctrl-Backspace should do this (un-pick) also but neither seem to work that effect. Version 220.127.116.11
Observed while following through the Tutorial 1 - navigation and User interface on the OSM structures layer
Things move fast (heaven help us with the next build...).
Esc is now enough, in 172.3. I think Shift-Esc was required in 172.0.
Esc alone is better.