Default software problem

Recently I installed ubuntu 16.04 LTS, but I have a little problem with it. I work with latex, and I use gummi to work with tex files. But when I set the default program for tex files to be gummi, all other text files, no matter the extension, and also text files with no extension, are opened with gummi too. But when I set the default program for all other text files to be gedit, then tex files are opened with gedit too. I didn't have this problem with ubuntu 14.04. What should I do? Thanks