I have added comments to https://bugs.kde.org/show_bug.cgi?id=238431 which might or might not be the correct bug to report on. xdotool mouseup 2 or xdotool mouseup 3 helps depending which mouse button up event gets lost.
** Bug watch added: KDE Bug Tracking System #238431 https://bugs.kde.org/show_bug.cgi?id=238431 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/505494 Title: Mouse events fail frequently and unpredictably, requiring kwin restart To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-evdev/+bug/505494/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
