Just installed 2.1.3. I cannot trim two overlapping rectangles to form one entity. After typing "tm" it invites me to select the limiting entity but I can't select anything. I've tried changing the "selected line" colour but nothing happens. Any ideas?
This is just a guess but the four lines in a rectangle, created by using the rectangle tool, may be treated as a single element. You could try exploding the rectangle.
In AutoCAD LT a rectangle created using the rectangle tool did act as a single element, or like a block, as I recall. If you didn't explode it and tried to erase one of the sides the whole rectangle would be erased.