Not sure if I am looking at the same place as you are .
Last weekend we upgraded from ontap 8.1.2 to 8.1.3P1 and just now I ran this command to pull the volume statistics for last 5 minutes i.e 300 sec and the latest data was being pulled fine(I queried for a volumes counter as below).
We are running oncommand 5.1 with the latest plugin for 8.1.3 ontap
dfm-hostname:~> dfm plugin list | grep 8.1.3
Storage System Config 8.1.3 R8.1.3xN_130608_0755 storage systems and vFilers
dfm-Hostname:~> dfm version list
list 5.1 (5.1)
dfm-Hostname:~> dfm perf data retrieve -o 159704 -C volume:total_ops -d 300
Timestamp 159704:CT_ctops4P_n01ora1_nosnap:total_ops
-------------------------------------------------------------------------------
2013-12-05 04:40:59 130.656
2013-12-05 04:41:59 108.083
2013-12-05 04:42:59 138.033
2013-12-05 04:44:08 156.391