Here is a screenshot, you can see that my mouse pointer is on the left of the sketch to pre-select the line, because I changed the parent part position (+ 10 on x axis)
The easyest way to reproduce it :
-create a part in the main assembly, and change the part placement (lets say you put Base.x to 10)
-create a sketch in the body.
-try to create a line in the sketch, you will see that when you click to draw one point, the point won't appear at the mouse location, but translated on x +10
It is like the sketch itself respect the transformation of the part, but every mouse event in edit mode
is still calculated from the origin, and not from the part Placement.