Amelia's progression is a bit messed up. While you're delivering her the dyes, you'll unlock midnight scenes with her (blowjob and sex through the hole in her door), but those can be unlocked before you call Kate to pose.
So the issue is that after a few times Kate poses, Amelia will talk to the MC and act as if they never did anything before. She acts "disgusted" when the MC blows his load under his shorts, and then even the MC acts surprised when she starts sucking him off, because she's his sister.
All of that would be fine, if the midnight scenes weren't unlocked prior to that moment. Those scenes did feel like they came out of nowhere too.
This game is excellent though, I love the writing, humor and art style, they're easily the best things about this game.