I decided to record a video to show the behavior exactly. Sorry for the low quality and shaky camera, I just used my crappy smartphone.
The template I used in the video is:
Code:
{author}{series:| - | }{series_index} - {title}
As you can see the resulting filename is not in line with the template, I even tried just making the template the word "test" with no fields so all the books would have the same name but the result is always the same:
Book name - Author(some number)