One of my French workbooks has these two sentences in separate sections: J'ai vu les moutons traverser la route. La police l'a aperçu entrant dans un laboratoire médical. It seems to me ...
Page 49 dans Advanced French Grammar, V. Mazet soutient ceci : A few present participles undergo a spelling change when they are used as adjectives or nouns. These include: —ant to —ent, —quant to ...