I recently had a client that had expansion on the Year dimension for a column in the report, and every time we clicked to expand the report, the rows would shift. The data no longer matched the rows.
I got the skinny from Oracle that there have been some bugs in FR (this particular release was FR 184.108.40.2067) with reports that used the Planning Connection and turned on #missing blocks on the report. The client installed the 220.127.116.11.511 patch, and VOILA! No more wonky rows.