Hi,
thanks for your post.
This happens, because you entered a huge amount of HTML code (for a table) into a table cell. That code contains line breaks in it, which get transformed to HTML <br/> tags by WP-Table Reloaded (a behavior that is intended for text, but not really nice for code, unfortunately).
So, what you will need to do is: Remove all line breaks from the HTML code in the cell. So, basically, your code should be in one line (except for those that get added by the browser due to the width of the textarea).
A better idea might be to simply use another table in WP-Table Reloaded for your table with content and then put that table's Shortcode in the outer table.
Regards,
Tobias