Endermen dont drop ender pearls when you kill them with fire aspect

I went to the end to get some ender pearls with my looting III and fire aspect sword and killed some endermen. However, i noticed that i barely recieved any ender pearls from the endermen. I didn't had a problem with this when i didn't had fire aspect on my sword, so im pretty sure it has to do with the endermen burning in flames. I tried my sword on other mobs, and it worked fine. Can you please take a look at this mojang, thanks.