To verify: Go to cgi-bin/koha/serials/serials-home.pl. Verify that the header has following tabs only: Search subscriptions / Check out / Search the catalog and that a checkin tab is missing.
I think this might have been intentional as 4 options take up more space. I think it used to be only 3 tabs per page, but now sometimes there are more.
It is intentional. The assumption is that checkout and catalog search are the next most common actions after whatever the module-related search is (in this case a search of serials).