Comment 72 for bug 565981

Alexander Bürger you are hit by the bug. The number is negative because "object bytes" uses signed integer to store its value (I came to this conclusion on my own, so sorry if that is not correct). And because there is a leak, and the number never decreases, it reaches a point when the number overflows (the maximum signed 32 integer value is +2,147,483,647). It seams that the patch proposed here is not present in the official Ubuntu repositories yet. You should add the PPA form https://edge.launchpad.net/~ubuntu-x-swat/+archive/x-updates and test if it works for you.