Back when Diego first debuted in Dora, he had one voice actor. Then Diego got his own show, and a new voice actor. Diego's voice was in limbo for a while; Dora would switch off between the Diego actor and the original actor for a time (the only rationale apparently being that the original actor would voice the normal Dora episodes that featured Diego as a guest character, and the new actor would voice the episodes that were specifically crossovers with Go, Diego, Go!). Later on, the vast majority of the cast was wholly replaced.
And now, after Caitlin's whole Screwed by the Network deal, Dora has another new voice actress as of Swiper's Favorite Things. The new voice is extremely noticeable.