Hi Gary,
this is very likely caused by your theme.
The theme does not show posts/pages in their entirety on category overview pages. (Within the theme folder, this probably is in one of the files category.php or archive.php.)
The code to look for is "the_content()". Most probably there is some
function applied around it that strips the HTML from the text. (This is
actually a valid procedure for some projects, where the category overview page is, well, just an overview, but in your case it is hurting.)
So, you have several possibilities, I guess: Fix the issue in the theme, or change to a different theme. :-)
To really confirm, I suggest changing your page to the WordPress Default Theme and see if the problem happens there on those URLs.
Hope this helps.
Best wishes,
Tobias