I'm having this problem too. No mods, no CC. One of my sims got the Desire to Create Midlife Crisis. One of the tasks is to Start a Mural. I tried the above and re-purchased the DIY Wall Mural and had my sim start one, but it did not complete (does he have to complete the mural? If so, the task should say something like "Complete a Mural" not "Start a Mural."). He also has the task to Shape a Bonsai Tree 5 times. I purchased the tree for the purpose of completing this, told him to shape it, then had him re-grow the tree so he could shape it again. It should be marked 2/5, but it's still at 0/5.
I haven't tried the other tasks currently on his list yet, but I did complete one so far once I read that he had to go to a museum to view paintings.
The Sims Team
