I added this to bug 1062, but I'm concerned it will be ignored since that bug report is very old.
The problem is that the Ctrl-Break keyboard command is not passed through to the Windows guest when running on a Linux host. Not passing through the Ctrl-Break combination means that some programs like MS Access cannot be controlled as expected. In the case of Access, the break command stops execution of a query. Without this command, there is no other option for dealing with a hung or run-away DB query other than closing the entire VM. (Access does not let you close it while a query is being executed.)
I'm using 3.1.2 r56127 installed from the .deb onto Kubuntu 9.04. I'm running Win7 in the guest with the Guest Extensions enabled.