And just this mouse integration doesn’t work like intended in my case. Instead the cursor moves to the lower right corner of the guest system’s desktop and registers masses of clicks with both mouse buttons. So I ended up using my sandboxed XP by keyboard all the time when running the guest additions.

After I told him about these problems, as advised me to install the standard Microsoft mouse driver for a “PS/2 Compatible Mouse” instead of the Logitech driver I used. This solved my troubles.