URLs always turned into links

This seems to have started in the most recent Drupal 7 update (7.56) although it may have been there before that.

My URLs always get converted to links. Enabling or disabling "Convert URLs into Links" in full HTML text format does not make any difference. Changing Text Format to "Plain Text" (and ensuring "convert URL into Links" and all other filter processing is disabled and "Display HTML as plain text is enabled in that format) does not make a difference. Using a different web browser or using incognito mode does not make a difference. Clearing cache does not make a difference. I have checked to make sure the urls are text and not links in the source html. Downgrading module_filter from 7.x-2.1 to 7.x-2.0 does not make a difference

So as far as I can tell this is a problem in Drupal.