Have you tried detach the mouse, whilst restart VB ?
To see if guest is saving default of host during save settings process, or a similar glitch in VB making it not save/reset.
Also the bottom right VB can attach host keyboard and mouse to guest,if you've done this on another VB may need to alter it for the test.
Clarity - I mean use menu settings of VB for detaching mouse, not unplug mouse itself , eg; you then have 2 cursors one inside the guest, and other in the host machine. Clicking in the guest join/attaches them again, so to make restart, then detach quickly, not to click inside the guest until it restarts fully etc