RollerMouse double click regression from 16.04 LTS to 18.04 LTS, how to debug?

[Christoffer Holmstedt]

Yesterday I installed Ubuntu 18.04 LTS as a fresh install. Everything seems
to work on my Intel NUC except for double click button on my "Contour
Design RollerMouse Free 2". I initially filed a bug report against the
kernel [1] because I thought it was some kind of kernel regression but
after further debugging today the kernel seems to behaving as expected.
Instead I suspect something goes wrong from kernel input events to when
XEvents are emitted, but I have no clue on where to continue my debugging.

### Expected behaviour
When I click the "double click" button on my roller mouse; left button
click event should be triggered twice. This is used e.g. opening a folder
in Nautilus.

### What is happening now
Only one click is registered so to open a folder in Nautilus I need to
press the double click button twice.

### Debugging so far
"xev" and "xinput test <id>" reports only one cycle of "button press,
button release" when I press the double click mouse button.

"evtest" reports two cycles of "button press, button release" for BTN_LEFT.
See bug report for output [1].

### Questions
Somewhere between kernel button events (evtest) to XEvent (xev, xinput
test) something goes wrong.
1. Which applications are inbetween that could be the culprit?
2. How do I continue narrowing down what is wrong?

Any help is appreciated.

[1]
https://bugs.launchpad.net/ubuntu/+source/linux-signed/+bug/1767660?comments=all

Best regards
-- 
Christoffer Holmstedt
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