There is a workaround for the problem with the cut scene at the cave not being triggered.
[*] Complete all other quests and save the game.
[*] If you have a save before finding the alchemist's ingredients and moving them, copy the 2 story.* files from that save into your latest save, otherwise you can use
these files from a save at the beginning of the imp village.
[*] Talk to Altoflix in the north of the village (if required), then the chieftain's son to get the quest to find the alchemist, talk to the alchemist once (only) and head to the cave.
[*] Continue with the game.
For the cave with the imp, had you explored to the south east first you would have meet the imp earlier, and he would have told you to leave, letting it slip that he was there looking for treasure. The conversation in the north east makes a reference to this, even if you had not encountered him before.