In Exodus 34:1, God said He would write the second set of tablets like the first, but I was taught Moses wrote the second set. In v27 God tells Moses to write down the commandments, but He doesn't say to write on stone, and then v28 says "He wrote on the tablets" but doesn't define "he". It's easy to assume it means Moses, but v1 said God would do it. Maybe God and Moses both wrote on the tablets, God working through Moses' hands, or maybe God wrote on the stone and Moses copied God's words onto parchment or papyrus.

When something in the biblical text doesn't seem to add up, try examining your assumptions about the text. Something you were taught when you were young might be predisposing you to read something into the text that isn't really there..