One thing I have noticed is that if you move a control point outside the existing boundary of the shape, the X/Y/Width/Height values change accordingly, which seems strange to me.

For example, draw a rectangle, double-click to get the node editor, select "Move Control Points", drag a control point of the top-left corner of the rectangle to the left. You'll see the X and Width values change in the PP. Also, when you stop editing, the values in the PP reflect the maximum extents of both the nodes and control points of the shape rather than just the nodes which is what I'd expect. I wouldn't class the positions of the control points as being part of the position/size of the shape. This could be confusing. Maybe that's just me though.

The canvas has its own "granularity" that can cause nodes to jump to places you might not expect them to but you've got to be zoomed in quite far and the jump is nothing like the millimetre suggested, and it only affects the node you've dragged and not the whole line/bezier.

It might be helpful to know the exact value that the line has moved and what units the user is using at the time but I guess if it's happening "randomly" it might not be easy to get this info.