Using libinput 1.9.1 from Fedora 27 on Wayland.
Material: Wacom MobileStudio Pro (using the new Wacom Pro Pen 2).

Reproduction:
- For instance in Nautilus, click somewhere in the file window with the pen.
- Raise the pen so that it does not touch the screen anymore but stays visible by the tablet (i.e. hovering it at maybe 1cm above the screen).

Expected result: nothing. When clicking inside Nautilus, there may be a contextual event associated to where you clicked, but that's all.

Actual result: a blue rectangle appears and follow the pointer, as though you clicked with a mouse, then hold the click and drag.

This is not a bug in Nautilus. It appears everywhere where a click and drag can occur. For instance in GIMP, using a brush with no dynamics, click and draw, then raise the stylus 1 cm above the screen => the drawing continus and follows the stylus.

To stop the drag action, the stylus has to be raised further away until the tablet don't see its hovering anymore. Then when getting the stylus close again to the screen, the dragging is effectively reset.

I personally consider this a blocker bug since it effectively makes this machine unusable with Wayland. You just can't use the stylus because any action you do in any software is just considered as a drag action (for instance I can't click icons or windows in the overview as well because it tries to drag them instead of starting/showing them). And as you can imagine, a Wacom tablet without using the stylus, this is like an oxymoron.

I won't edit the severity though because I'm not the one to decide.