The islandora_solr_config modifies the query if you are using the grid display.
After setting the solrStart variable.

It changes the number of results to a number divisable by 3 and 4.

Using a default 20, means it changes to 24. But it never changes the pager.

So you display the last 4 results from each page as the first 4 on the next page.

ie. start=0 rows=24
    start=20 rows=24
    start=40 rows=24.
Merge branch '7.x' of https://github.com/whikloj/islandora_solr_search into 7.x