Inside the MCP, if a topic has posts waiting for approval on subsequent pages (2,3,4,etc) and these posts are the initial posts on that page, it will not be displayed when viewing the topic in the MCP. Only when an approved post is posted after these unapproved posts will they then be displayed.
Example: we have the default 15 posts on page 1, an unapproved post is waiting for approval on page 2, it will not be displayed in the MCP unless you select "show 16 posts per page". Setting the value to "0" (which should display all posts) does not rectify this.
(there are 3 posts per page in the screen examples)