Cake pop and fondant question/help

Wondering if anyone can help me out with this….I made some cake pop mini purses, about the size of 2 regular pops on a stick, iced them with buttercream icing put the fondant on and some of them the fondant started to get very soft almost melting, (they were chilled) I made 2 cakes one with oil the other with butter.. now I did not keep track of which was the butter cake, which was the oil cake. Do you think that the oil in the cake pop seeped out causing the fondant to do this?, were the butter is more solid which would not seep out right? Would the icing not stop the oil from seeping through?, if so why would a regular sized cake baked with oil not make the fondant melt? I did not want to use chocolate I think it would be harder to decorate with…not sure never tried

Thank you!!