When opening an old LO version html web page with linked images in the cells of a table,the links are shown properly. When saving this file in LO 4.7.7.4 of the latest LO 5.1.0.3 release, the file size is grewing heavily, because all the links are broken. When opening the file again, indeed all the images are embedded.
Also see bug 88038 -- WRITER WEB: handling of inserted images -- data URI embedding as base64 for email support, broke LO as HTML editor *** This bug has been marked as a duplicate of bug 48887 ***