This is a really arcane bug, as most people will write it off as a hardware. I first thought it was a wireless mouse issue (started by changing batteries) it's only after observing it for a while, you can put the pieces together. I think I finally made the connection a week ago ... http://ubuntuforums.org/showthread.php?t=1335101 --- hi guys, I've posted with an experience with 9.04 which I originally thought was a mouse driver issue. However a recent incident has caused me to suspect a misdiagnosis which may be why I have't gotten any answers. The problem is intermittent (the worst kind) and revolves around the mouse. My system is dual-boot with XP, and XP works flawlessly, so we can eliminate the mouse hardware. However, it's a Labtec USB wireless (with keyboard). The problem manifests itself by mouse clicks not working. Initial thoughts are the clicks are being ignored, as the pointer moves around the screen. However, a more detailed inspection of the situation reveals that it's not that the mouse clicks are being ignored. It's that the system appears to have "trapped" the mouse focus, as moving the mouse over buttons no longer causes a highlight. In firefox (for example) hyperlinks no longer cause the cursor to change to a hand. The problem seems application independent ... happens in Nautilus, Firefox, NXClient (that ones a killer as it gets trapped in the NXClient window, and you cannot break out of it). When the problem happens Alt-Tab also stops working, so you can't switch windows. At first I suspected (obviously) a mouse/USB problem. However, on Friday, my Linux-expert brother had caused to VNC into the machine, and the problem happened to him. Which pretty much lets the hardware of the hook. At his suggestion, I switched from GNOME to KDE, but the problem still happened, which narrows things down to the X-Server ? (Notice the question mark - I'm a Windows programmer, so the intricacies of Linux/X-Server/Desktop environments is all a bit of a dark science to me). Moving on from here, I have noticed one set of circumstances which appear to guarentee the fault happening, and which may explain the intermittent nature of the fault. It seems to happen when the mouse focus passes into a list control (NOT a drop down list). I noticed this after opening the LogFile Viewer, and realised that the mouse focus was getting stick in the LH pane, which lists the available log files. Once it is stuck in there, it won't allow clicking anywhere. However, interestingly enough, if I hover the mouse over the right hand side (the contents of the logfile) I can hold the mouse button down and highlight text - so clearly the system is "getting" the mouse click. However moving the mouse to the "Close" button and clicking does nothing - no highlight, no click. For those of you that know the "Blueman" app (for bluetooth) I also noticed it here ... when I click the icon the app comes up, and works fine, except if I click in the list of plug-ins. Then the mouse gets trapped .... So there you have it ... This problem is occuring on two 9.04 installs, one an upgrade, and one a fresh install. The fresh install is my sons "mess-around" copy, so yesterday I decided to upgrade to 9.10 and see what happens. In the meantime my system is still unstable So there you have it. The most detailed analysis I could pen. Ideally someone will step up and say "Ah! That's ....." and give me a fix. Failing that, if someone could point me into the direction of somehow enabling some debug, and a file to look into to see what is happening, I'd be eternally grateful. For any Win32 heads out there, the best way I can picture this bug is that once the mouse focus moves over a certain graphical object, then the message handler somehow manages to crash and mouse click events are not forwarded down the chain. However my brother (who is also not an X-server expert) claims Linux handles events differently to Win32 ... --- So what do we know about this bug : 1) It's sporadic. I've had it occur as soon as logging in, othertimes I can have a 30 min session and not see it 2) it's application independent 3) it *may* be connected with a particular GUI element ... scrolling lists appears suspicious. 4) even when the bug isn't apparent, ALT-TAB doesn't work for me 5) I don't have 2 monitors. However I will check that Xinema is not doing anything on my system (posting from work) 6) It's hardware independent. I have seen it on my machine (nVidia) and my sons (Intel) 7) It has nothing to do with Compiz, or metacity or GNOME 8) it appears to be in the XServer, as a remote VNC connection has the same issue ? 9) it has lurked in various Ubuntu releases. I saw it occassionally in 8.10, but it was so infrequent I put it down to my having done something wrong. It got much much worse in 9.04, and seems to be no better in 9.10 I've posted here as you guys are clearly more au fait with the guts of Linux, and I am willing to do any directed research you suggest - so if you can suggest a debug/tracelog I can run for you, go ahead. This bug is a system-killer. I could not in all conscience recommend any Ubuntu system post 8.10 to anyone needing a stable system.