Found out a bug in the library when using the Author sort. I use calibre to send my books to the kobo, using the metadata plugboard so I am able to have the title changed to include the series and number of the book. But when sorting by Author, every book for the same author should be sorted by name (just like the original kobo). But it seems to have a mind of it's own.
I also tried different naming format, for example instead of "Series  - Title" I tried "Series - 01 - Title", which did not change anything. Also please note that I did this for both the title and title_sort field. Also tried to delete and send the book back into it.
Also when doing a search for an author the screen that comes up is sorted properly (probably because they are sorted by name in that screen).
I have also tried to just copy the books manually and the same thing happens, so everything points to a Kobo bug.