From my experience in WF5/Creo, the surface that the balloon is attached to is not showing up in the secion view therefor the balloon cannot attach to anything in the secion view. It's a pain, but if possible Move Item To View and select one of the none section views. Edit Attachment and point the balloon to a surface/edge that will show up in the section view. Move Item to View to move the balloon back to the section view.
The second option is to delete (not erase) the balloon and create it again in the section view. This should force it to find a surface that is showing in the section view.
See if this helps,
Thanks, Dale