Why two different endings? I guess the difference is that the participle takes on the e ending when used in a participial phrase and the i ending is used when the participle is used as adjective but beyond that I am not too clear. Thanks.
I think you are on the right lines.
This is what Gildersleeve has to say:
Ab. amante (ī) etc
83, REMARK.-In early and late Latin, and at all periods in the poets, we find -e is often found for -i in the Abl. Singular. In classical prose we regularly find compote, dēside, impūbere, participe, paupere, pūbere, superstite, vetere, and frequently dīvite (but always ditī), quadrupede, sapiente. With participles, -i is usual when they are used as adjectives, but classical
prose shows -e also in antecēdēns, candēns, cōnsentiēns, dēspiciēns, effluēns, hiāns, imminēns, influēns, profluēns, cōnsequēns (but sequēns, not before Livy), titubāns, vertēns.