Multiple authors not showing in Kobo

I noticed today that for some time (1 month?) books with 2 authors (at least) show only one on Kobo Glo when transferred in kepub format. Since I have a new installation (new laptop) I wonder if something was broken during the transfer, although I restored the config files and settings. Another possibility could be a change in Calibre or (less likely considering the last update date) in the Kobo Touch Extended driver. Any idea?