Awesome, thanks for the details. I think I should be able to address most of these easily.
1) Likely just didn't set an actor's sprite sheet.
2) That's a bummer; that's honestly a downgrade of a reward for finding that secret! I must have forgotten to swap the actual reward after copy+pasting the chest/script.
3) Should be easy to adjust the timing.
4) The magic spells will only fill the next most available slot and you can learn them out of order, but that made the logic tree pretty long, so I most likely just forgot to have the scenario where you have learned flame first but no others forget to erase the frost text too. Seems like the buttons work correctly since you can't select it, just a visual glitch (and spoiler that Frost is a spell :P )