filter is not working on task report data

I am trying to use work with below snippet, the filter is no applying on process analytics.
With or with out filter is giving me the same result.Here filed "c8" contains Assigned To values for the task(i.e user(s) /group(s)).
Here I am trying retrieve the tasks assigned to particular group /(user),but it is fetching all the tasks.
a!queryProcessAnalytics(
          report:cons!TASK_REPORT,
          query:a!query(
                    filter:a!queryFilter(field:"c8",operator:"includes",value:togroup(876)),
                    pagingInfo:topagingInfo(1,-1)          
          )
)

OriginalPostID-244965