I recently made Mike Pekovitch’s dedicated sled for mitred boxes (Tools & Shops #286 Tablesaw Sleds for Joinery) complete with the split-level base.  I have  a problem with a piece of residual stock that is left on one face.
When I make the first cut from my stock it leaves a clean mitre.  However, when I make the second cut to sever this first side of the box completely, this piece is effectively floating off of the split-level base and is unsupported.  It drops down under it’s own weight marginally before the blade has completed the cut, leaving a little un-severed piece on the mitre face.
It does this each time – one good face the other not.
I thought it was perhaps to do with the height of the saw blade, but I have since raised it to the maximum I can safely do within the sled and it is still causing this issue.
Another thought was is it the type of blade (AFB) and would a flat ground make a difference?  
I have watched Mike’s video and his piece drops away with a clean face so can anyone help me with what I’m doing wrong?  Thanks.