A quick Google shows that the statoverride file is used to tell dpkg to use a different owner/mode for a file when installing a package. The file on my system is empty, and I don't know why you're getting anything written to it. If you're not manually doing something, then presumably one of the packages you're installing is editing the file as part of the install process. Installing random .deb files without knowing exactly what you're doing is generally a bad idea.