There were some bugs in solver as most of constraints that were added can create crashes (like the middle of edge creates internally a wire check that makes that things to work nice for a line, but not that nice for a rectangles). On the same manner there was fixed the crash when setting up an axis coordinate based on a point coordinate given the fact that an axis and a point3D are different shapes even they can work on the same initial location.
Middle of face (for rectangle and rectangle2p) was also seem to work right now.
A design limitation I want to get it right is to apply more constraints on the same node that a small fix was done, but the code was not yet commited as need more testing. Also horizontal line and vertical line are just one way integrated, meaning that those lines are registered in solver and they can follow points from lines (in general) but they are not constraining none of the generated geometry (yet).