This is a known bug. One that has been mentioned several times on the Ubuntu and Linux Mint forums as far back as July this year, and maybe even earlier. Honestly I don’t remember this happening on my old desktop computer – Intel Core 2 CPU with a 250GT NVIDIA graphics card. Lately, I’ve been having these lock ups one too many times since I purchased my notebook barely a month ago – Intel i5 2410 with dual GPU (Intel HD Graphics and Radeon 6470M). On both desktop and notebook, I have Ubuntu 11.04 installed with the main difference being, aside from the hardware, that the notebook sports the 64-bit version to fully utilize the 8GB memory.
The bug seems to happen randomly with LibreOffice (LO) running. In my case I use Calc more often than any other LO app so my experience with the system freeze is solely limited to Calc. Other people, however, report that they have experienced the same thing with Writer.
I am not sure how to reproduce the bug. On most days LO Calc is fine. I almost use it on a day-to-day basis. There are just those few occasions that it freezes the system and today is one of those days.
Today I had to force reboot my notebook three times in less than half an hour because 5 to 10 minutes into doing a few simple operations with a .XLS file – such as copy pasting a few lines of text from one file to another – the system locks up.
After searching about this problem on the Internet for a while, I was finally led to these particular threads on the Ubuntu and Linux Mint Forums – http://ubuntuforums.org/showthread.php?t=1813246 and http://forums.linuxmint.com/viewtopic.php?f=47&t=77851&p=456737.
The suggested fix is to disable hardware acceleration and anti-aliasing on LibreOffice.
I cannot confirm or deny that this supposed fix was effective in my case. So far LO Calc has not misbehaved after I disabled the Graphics Output options from the LO View preferences. One thing to note is that among the few things in common with the system freeze as experienced by the others as mentioned in those threads listed above and mine are that the graphics card in use is Intel HD Graphics and on an Intel Sandy Bridge CPU.
As an added precaution I have made sure that LibreOffice is not using a Java Runtime Environment.
Again while I am now sure that LibreOffice is the culprit as to why my system locks up randomly all of a sudden, this does not happen that often. Yes, it may have happened one too many times to be noticeable, but it NEITHER happens every day NOR does it happen at the frequency of at least once every time I use LO. Always, the system freeze happens with LibreOffice running and always at that time when I am working on it.