Can't resume writing song with guitar in inventory

I have a sim partially written song who, when I tried to click on the song to resume, it was greyed out because "there is no guitar here". He had one guitar in his inventory, and another guitar was in the household inventory. When I place the guitar from household inventory on the lot and clicked on the song to Resume, he started using the guitar in his inventory.. Since he was aware enough of the guitar in his inventory to play on it when there was another guitar on the lot, he should have been aware enough of that guitar to play on it without another guitar on the lot.