I believe (but not sure) this is a Cinnamon specific problem, because I haven't experience this in KDE/Gnome.
When I need to click and drag the mouse, like dragging to move files, or highlighting text in PDF files, I have to click and pause for a moment then do the dragging. Or the starting point of dragging will not be the place I just clicked.
On the second line of text, I clicked and paused for a fraction of second, then drag the mouse, everything went perfectly as I intended.
I do the same thing to the third line, only without the delay between click(mouse down) and dragging. Notice my mouse was down on the first character of the third line, but the highlighting only appeared a few character later.
This mouse lag effect is global in system, I mis-moved some files, and used wrong components when I was using graph editor(yEd).
I don't know if I expressed the situation correctly. Did I break my system or is this a bug?
ED: to explain this in another way, it's like the system need to record the mouse coordinates when I press the button, but there appears to be a time lag between mouse-down action and the actual registering of coordinates. The result is registered mouse-down coordinates may not be the right place when the mouse was clicked, because the mouse was moved.