...bsms, I get what you're saying, but if your purpose behind posting random internet photos of riders with their feet in the "home" position was to show that some people ride that way, here are a few more that I found to add to the collection.
Now how do we know that they purposely wanted their feet on the "home" position during that exact millisecond of time that the photograph was taken?
Good point. Those Australians waiting around ALL just accidentally put their feet home - at the same time!
And cutters do it accidentally too, I suppose.
And the cowboys of old ALL did it by accident, eh?
Gen Patton, accidentally letting his feet slide forward:
Actually, if you would READ the link I provided, you'll find a number of people do it deliberately. But then, reading a link before commenting seems to be too much to ask of folks.
From the perspective of the OP's problem: The folks who tend to deliberately ride with their feet "home" do so because their activities make them value keeping their feet in the stirrups more than having the hinge of the ankle working for them. And as I pointed out, when I'm on a horse that I don't fully trust, "I unconsciously put my feet much further into the stirrups
Thus, if the OP tends to have concerns about keeping her stirrups, then she may be subconsciously pacing her feet further into the stirrups.
"as soon as I kick the horse on, change transitions, post in the trot, my whole foot slips through the stirrup"
Might suggest the stirrups are too long for how far her legs stretch on that particular horse. Or it might be, as I pointed out in my first post, the boots she has make the stirrups slip and, again, she subconsciously homes her feet to keep the stirrups.
If the OP is riding for competitions, then it is a problem that needs solving. If the OP rides for fun & function, then she can decide if it is really something she needs to worry about.