Click and drag on ThinkPad T480s doesn't work

Hello,

I'm reporting an issue with the touchpad of a new Thinkpad T480s, that forbids to drag or select objects with a one hand click-and-drag movement. Actually I don't want to repeat it here but quote from a report filed by Jakub Schmidtke over on bugzilla, who reported this issue before me, summarized the behaviour nicely and even created a record of the events in question:

"Under Windows, as well as on my old laptop, when I click on the touchpad and keep it "clicked" with one finger, I can then drag the object with my swiping with my other finger. On T480s it doesn't work. The cursor doesn't move at all, although I can see it changing shape when the drag happened on the top bar of a window. (...) I attached a recording of that event - this is a click and a drag down-right a little bit. When I do the same thing with my mouse, it moves the window. With the touchpad I saw the "dragging icon", but the window did not move."

Please find the full report and the recorded event here: https://bugs.freedesktop.org/show_bug.cgi?id=107952

I want to add that the trackpad worked as expected before I upgraded my Pop!_OS (Ubuntu basically) from 18.04 to version 18.10, though I did not notice the changed behaviour immediately, so it might be due to a subsequent update in the following days. It is reproducible on Fedora 29 as well.

I know the libinput documentation has a paragraph on very similar touchpads used in the 2015 Lenovo X1 Carbon 3rd series where the entire lower area is registered as one big click area and "without any positional finger data and it is impossible to determine whether it is a left or a right click. libinput ignores such button clicks, this behavior is intentional." The click is not ignored though, it is executed just fine but the movement of the second finger is not processed (which would make sense somehow if there is no position data available on the lower click. but why did it work before?).

Thanks! Paul