Ubuntu Mate 16.04 mouse inputs not handled correctly on multi gpu system

[technomage bruce]

  My mouse inputs aren't being handled properly by a few but not all applications in Ubuntu 16.04 using the Mate desktop. The problem occurs on my system that has 3 gpus, 5 monitor setup with compiz, accelerated graphics, and xinerama enabled. I'm using the Nvidia 361 drivers. I do not have these problems on my laptop, a single monitor setup with compiz and accelerated graphics enabled.

  Applications like the Caja file manager handles all the mouse inputs correctly, but the Dolphin file manager doesn't. In Dolphin, I can mouse click the menu items just fine, but any sub-menu mouse inputs are not registered. Also in Dolphin, none of the mouse inputs are recognized while clicking on any of the files/folders/places but I can still use the mouse to scroll the file list window.

  Other applications that exhibit this odd mouse behavior are VLC and SMPlayer (see https://bugs.launchpad.net/ubuntu-mate/+bug/1637020 for a bug with VLC that I filed that I believe has a similar root cause). Other applications that I've used that don't exhibit this behavior are firefox, chromium, virtual box kaffeine, tvtime... actually, all the other programs I've tried don't have this problem. I'll update the list of problem applications as I come across them. My *guess* is that the common denominator between these problem applications is that they use the same graphical tool kit and that there is a flaw in that tool kit's implementation that affects multi-gpu systems.

  If you want, I can record my desktop to demonstrate the problem.

[Martin Wimpress  (flexiondotorg)]

So far, you've not listed an application from the MATE desktop as being affected by this issue, in fact you specifically state that Caja (the MATE file manager) work correctly.

I also have no way to reproduce this issue given your exotic hardware configuration :-(

[Sebastian Ramacher (s-ramacher)]

Sounds like a Qt issue (similar to #1637020).