FBR General Discussion, page-7434

I believe that was due to the slab not being inside the tolerances FBR are used to working within. Generally the slab is poured withing 5-10mm across the entire dwelling and then sanded and levelled before the build to allow the first row of blocks (and every course there after) to be sound.
i would imagine that in this instance we don't know who poured the slab and if it was within the tolerances FBR are used to working within.

...to put your mind at ease I do believe slab pouring will be a future iteration to incorporate our DSTechnowlogy which will ensure an accurate pour every time. No levelling of slabs, no sanding and no chocks, spacers or wedges.