Bethlam you're right! I was talking about the SEWING HUT! When the villagers go for jogging and go near it, they start running from the hut to hospital again and again and they can't finish their "exercising program". To gain their skills they must run all around the island and finally seat between the fire and the table of the reserchers. Otherwise they DON'T GAIN THEIR BUILDING SKILLS.
At least in my game I noticed this glitch many times.