Child Theme functions.php breaks WP image uploader
I have the Vantage theme installed, and a child theme working fine. I need to add a couple of lines of code to functions.php, so I created a child functions.php file in my child theme directory (..../vantage-child-theme/functions.php)
However, when the functions.php is present in the child theme directory, the Wordpress image uploader stops working. That is, if I choose 'Add Media' on a page or post I cannot see the media library tab, and I also cannot properly upload by selecting files from my PC. Trying to upload gives an error saying 'An error occurred in the upload. Please try again.' I do not get to the image properties panel. However, the image IS actually uploaded, as I can see them by using Media > Library from the WP
The interesting thing is that the mere presence of functions.php in the child theme directory is enough to cause this, even if the file only contains the opening and closing php tags.
with no actual code inside.
Am I doing something wrong? Is this a bug? I have tried it on a clean install with no plugins...