Thanks for the explanation.
While testing the "rectangle by 3 corners" tool I noticed another strange behaviour.
If you start typing the rectangle by fixing all variables ("x of the 1st corner", "y of the first corner", "length", "angle (to HAxis)", "width") except "angle to the first edge", then move the mouse to find a suitable value for this variable and block it by typing its value in the input field, you get a completely different geometry than previously suggested in the preview.
This is what you see in the preview with "angle to first edge"=135°: and this is what you get after typing in the value: The same happens for the "rectangle by center and two points" command.