Unable to add comments to text in Pages object captions

I am using Pages to edit a draft of an illustrated children's book. When I suggest an edit to some text, I use the "Comment" icon above the page to add the comment. However, when I suggest an edit to some text in an object caption, the "Comment" icon greys out. Does anyone know how to add a comment to text inside an object caption? I've searched the Community but have had no luck finding a solution there. Please help if you can. This is very frustrating. Thank you.