I'm only guessing here but I think you had one of the end points constrained to the origin.
You can easily add a coincident constraint on one of the corners
OR as I prefer add horizontal and vertical constraints to the center marks of the lines of the rectangles.
No I always draw teh rectangles like this then add 4 dimensions the horizontal and vertical overall lengths then distacnce to center. Now it wants me to constrain the 2 vertical and 2 horizontal lines. as well as dimensioning the lines.
Accudyne1, I couldn't reall read your screen shot here but with me switching back and forth from classic to ribbon interface style the problem was fixed.
The actual image was attached also, but glad you fixed it. I am guessing it was constraint inference/persistence. They must have gotten toggled off at some point.