I was playing in Blender and did something that froze up the system. (I think I set the samples rate too high). Eventually, I had to reboot the system as it was completely frozen.
When I restarted (with the system reporting it had not stopped the watchdog), I found the mouse was displaying weird behaviour. I can't click in multiple areas of an application, without switching between desktops. For instance, if I click the left pane of file manager (thunar), I can select a directory, but clicking in the right hand pane either does nothing, or selects a directory in the same horizontal space in the left pane (as if there was no right pane). If I switch to another desktop and switch back again, I can then click in the right hand pane, but no longer in the left hand pane.
The effect is similar if I click a button in the application's toolbar. For example, If I click the up one directory arrow in thunar, I won't be able to click either the directory or file panes until I switch in and out of the desktop. Similar behaviour occurs in the browser - I can click in the navigation area, or on the tabs or a link in the content, but once I've done one of those things, I can't do the others.
Sometimes, when I can't click at all (ie there is no change when clicking), I can right click in the window and I get a context menu about the workplace switcher, with 'Properties', 'Move', 'Workspace settings...', 'Remove' and 'Panel' options.
Scrolling doesn't seem to work properly either. I cannot scroll browser windows, file manager windows etc. In VLC, scrolling no longer scrolls through the playlist, but instead changes the volume. Using the MMB in Blender now starts the Anim Player and doesn't move the drawing object in the viewport as it's supposed to.
I have rebooted, tried changing mouse drivers, connected the mouse to a different usb port, all to no avail.
i7, running Arch linux with xfce desktop.