The functions.php file is used to hook into both the front and back ends of the website to customize many parts.
the_content is a filter which should only be used on the front end of the website. As in, shown in a page template, not shown in the wp-admin.
Can you please confirm what version of ACF you are using?
You mentioned ‘Tab_content’ is referring to the tab content (WYSIWYG) in the Admin folder. So am I right to assume the problem in the backend (wp-admin)?
I don’t know what <?php build_i_world_map(1); ?> is but it shouldn’t be related to this issue.
The original code should only modify the WYSIWYG value on the front end of the website (page template), but should not ever have changed the value in the backend. The backend should have had no changes from the code.
If you are running ACF v4.x.x, then this is the wrong code. Please use format_value_for_api, not format_value and this could explain why it is being run in the backend.