Windows Museum collection - in game achievement and stardrop not dropping

[paupau]

I've checked that is completed, and the only dialogue I get from Gunther is “The museum looks amazing! Thanks again for all your help.” I think the problem might be similar to this: http://forums.stardewvalley.net/thr...-but-game-says-im-missing-one.3746/post-23498
I've also tried it and it doesnt work :(