Not sure whether anyone else has had this same problem.
I had previously changed the database table default prefixes from wp- to a custom number as recommended by WP to prevent hackers. However, since the last WP update I have found that each time I apply a custom page template in my theme to a page on my website it changes my custom number in the DB of that particular page back to its default of wp-.
If I then edit the wp- and change it back to my custom number, it changes the custom page template in my theme back to it's default (ie. Default Template) and I lose all the customisations of the custom page template.
I've tried changing the database table prefixes I was using to a different number and also re-created a new wp-config.php file and changed themes to rule out the problem being theme-specific—all to no avail.
Perhaps something is over-riding the wp-config.php file? Does anyone have any ideas what the problem could be and how it could be solved?