Davide Ferrari reported this bug in version 3.2.7:11 of procps. I think the problem is due to change in format of /proc/diskstats since version 2.6.25 of linux kernel. Lines with partitions information have the same number of columns than lines with disks information since this version of linux kernel. They had less columns in previous versions.
Newer versions of procps (in particular 3.2.8:10) work properly because this problem is fixed by vmstat_part_format.patch. Alfredo
