Just a thought here guys, with emulsion paint that goes back to a "liquid" state when wet, could it be that a lot of tilers now-a-days are using rapid set cement addy and doing so just "damps" the paint surface long enough to make it unstable and then the addy is set to an unstable surface. With bucket stuff, White Star for instance, the addy is wet for much, much longer has more time to "soak through" the emulsion and bond to the substrate behind.
Only reason I pose the question is that I have removed tiles from painted bathroom walls and it has come away with large amounts of substrate attached to the tile. The addy has quite obviously adhered to the plasterboard through the paint in most places though not all. Not sure of the reason for this.
Thoughts on this guys?
Grumpy