I can say there is at least two reasons that changing stake does not matter, either its a mistake that it dont keep track of each stake separately, or its not random and it can control when its triggered.
Being able to change stake at will would open the door for stake manipulation at the very least if it was random, so it will almost certainly be changing the odds somehow to protect against that.
These predatory games should be banned IMO, and the UKGC should look into these type of games very closely as 100% all will not be as it appears to the player on these.