P.S. That makes sense, if you have version Prestashop 1.4
In the PrestaShop 1.5 you can't use image caption.
Store uses Product name instead of image caption - see screenshot -
http://screencast.com/t/a5sVX3xlhD9
Please try yourself to change product name in the PrestaShop Backend.
Image caption can not affect those tags (title, ALT) :-(