I, either, have never seen ふんとする. ふんとする indeed exists, but this is a classical expression. I checked ふんとする, including 芬とする, 紛とする and their inflections in a corpus. The only one search result is the following sentence in a novel written by 泉鏡花.
友だちは持つべきもの、緑蝶夫人といふ艶麗なのが、つい近所に、家内の友だちがあるのに―開けないと芬としないが、香水の薫りゆかしき鬢の毛ならぬ、衣裳鞄を借りて持つた。
He is a novelist in Meiji and Taishō period, i.e., a hundred years ago.
It seems to me that it's a typo or misreading of ぷんとした with the same meaning.