I have an Chromebook running Ubuntu with KDE Plasma in a chroot through Crouton. I recently updated it to 18.04 which I believe is unsupported right now so this might be futile because the kinks simply haven't been worked out yet.
The touchpad has an unusual malfunction which I haven't exactly pinned down yet. In some contexts, when I tap, release, and then drag, the mouse continues to hold down. For example, in Dolphin, if I drag the mouse across the screen, it selects a box, the way you would expect it to after a double tap. I can't figure out how to get it to release mouse and stop highlighting when I move the mouse around.
In other contexts, like a textbox, a deliberate double-tap and drag seems to give up and release automatically after a short period of time (less than half a second. For example if I tried to highlight this paragraph by doubletapping at the upper left and dragging down to the corner it would only highlight the first few words. If I double tap and drag in Dolphin, the cursor only starts highlighting after half a second. I'm not sure what to make of this.
There is also a touchscreen. I have no reason to believe any inputs from the touchscreen are interfering here.
I have tried to use xev to debug but I don't think it is capturing the data I need, such as whether a click is being held down through a drag.
I am on a Chromebook like I said and I don't think the limited functionality of the chroot allows for virtual terminals within it. So I can't figure out how to run evtest because I don't know how to get X to release the touchpad.