Preview tabs auto switch – Ask Different

So this is a feature that is quite annoying. I am trying to read a math textbook and the layout of the book is such that the answer sections and the questions are in two separate parts of the book. So usually what I do is I would duplicate the file using and then swtich between tabs. But recently I find that for whatever reason, Preview decides to auto switch between the two pdf file automatically. Is this a new bug and how to fix it? Thanks in advance.