How are those captions added? We have both title and description for images ... Popup would only display the title I believe. Let me know how you added them, and I will take this into consideration when we work with the forthcoming improved popup module.
I added them using my photo software... IPTC Description field. I am also hoping that Panel 2.0 will allow me to add the IPTC Description to the image.
Alex
https://www.merelyafleshwound.com
https://www.goldenbikeshop.com
I believe the gallery layouts support title/caption+description, while the popup only supports the main caption. I will try to fix this for new popup coming soon ...