Was the area of the tiled floor that is still stuck down trafficed much before it was tiled?
The reason I ask is that a few years ago I was on an Ardex/BAL course and this topic came up. They said that one of the major issues with certian Plywood boards was that they are coming from really hot climates and at first the plywood was arriving in the UK having spent weeks or so in very hot temperatures while in transit. This caused the glues that bond the plywood togeather to melt out of the ply to the board below while they where in the hot climates and when the bales of plywood were taken of the boats in the cooler UK they ended up as one large block of useless plywood all stuck togeater as one.
To counter this the manufacturers in these countries treated all the boards with a releasing agent that prevented the boeards from sticking togeather during transport. These releasing agents are invisible so they reccommended that before tiling any ply the board must be thourouly sanded to remove the releasing agent which in turn would allow the adhesive to key properly. I'm wondering if the area that the tiles are still down on had enough wear to remove the releasing aget before it was tiled?