i think what matters most is how 'activly' a persin resists in a will save. If it;s a case of them consiously asserting thier will ("thog does NOT like puny wizard!"/"thog knows their is no wall thier!"), then the feeling would be very hard to confuse with anything else.

if it's just somthing they do without thinking, then they may no recognise they made a save, as Bendraesar argues ("puny wizard makes thog fuzzy as he stuggles helplessly..../"are you ignoring orcs their behind glostly wall?").