On the demo eg. here Row Evolution for a Social subtable will show that all past periods had "1" visits.
It seems to work for month/week periods so maybe the bug is only for year.
Note: It is useful to fix this bug, because I am thinking the code for Social table, which creates the "datatable view" of another report (getWebsites) could be reused by other plugins later, to create "Views" of any report in Piwik, so we might refactor this code and make it reusable for plugin developers later.
Looks like it works now! NICE