Please try the following :
In the "SequenceFilePostStep" copy the processed data to a stationglobal or fileglobal variable.
In the calling step properties add this variable in the additional result (properties-->additional results).
I checked with TS 13 it reports properly.
Since the "SequenceFilePostStep" is an engine callback probably it may not support updating the report .
Hope this helps.
Ravi