Ann: Total Depth reached & additional zones of strong gas shows, page-164

I personally think that is why they TD a bit early and way earlier than the 4000m quoted from the AGM.
I think they are concerned that the mud weight may cock up reservoirs shallower or start playing funny buggers with the clays again.
Just my take any way.
I'd also guess that they prepared for this so were expecting it given the 6 inch tools ect. I'd like to see them case it to where we are to protect the flow test, which I'd bet is what will happen, then drill on. If the hole shits itself below the casing it won't matter....unless they get those expensive tools stuck.