Submissions to group; only last five submissions display

In a Controlled group page, under heading "Submissions to this group", only the last five submissions are listed. Clicking on the link for the Next page displays "undefined" under the same heading; we expect to see earlier submissions. Even if there are 35 submissions (generating estimated 7 pages) links for only two pages are offered.

Link on 2/Next/Last: https://[mahara]/group/view.php?id=723&group=723&editing=&offset=5

Steps to reproduce:
1. With a user (teacher) with Site staff role, create a controlled group.
2. Add at least six users (students) to the group.
3. Logging in as each of the students in turn, submit a collection or page to the controlled group. (You may wish to view the list of entries under the group's 'Submissions to this group' heading as you go.)
4. When you've submitted more than five collections or pages, the link to page 2 / Next will appear. Clicking on the link will display the Group page with 'Submissions to this group' = undefined.

Mahara 15.04.1, Linux, mySQL
I believe this is our first use of a Controlled group in this way since we upgraded a few months ago from v1.9 a few months ago.