In some of our HTML content we have anchor links, unfortunately the regex that is built in filter_save_ignore_tags seems to have issues with empty tags.
I believe this is because inside the tags it's doing (.+?) - Now I'm not a regex expert, actually far from it, but as far as I can tell that requires at least one char in between the open and closing tags.
I've fixed this by changing (.+?) to (.*?) which seems to work in all cases.
Could someone look over this fix, and if it's correct commit it to core.