Uhm...I would think the spirit is actually Force 6, and comes in as Force 2. When you leave the background count, everything returns to its former Force. If it isn't, then everyone will just always summon their spirits and cast their spells before entering the background count.
EDIT: So, yeah, just went and checked it, and you are exactly correct as to what happens. The spirit is Force 4, so it enters at no Force and is disrupted. and then your reputation with the spirit world is harmed. Spirits are insanely vulnerable to background counts. So, cast your spells and summon your spirits beforehand.