Where to begin?
I didn't see what happened with Casey.
Dick, the reason you didn't see Weaver's ball move on Friday was because his didn't. Michael Thompson's ball definitely did move on #15 though.
On to what I've read about Casey from above.
If his ball did come to rest in a depression, he could mark the ball and lift it. If the depression was clearly a ball mark or old hole plug he could fix it. If it wasn't he couldn't. Did he fix it?
Now, if he didn't fix it he would have to put his ball back in it. If he didn't and he hit the putt, he would be liable under Rule 20-7 for playing from a wrong place and be penalized two strokes under Rule 20-3.
But, if he tried to put his ball back where he thought it was and it wouldn't stay there, he would have to find the nearest spot where it would stay that wasn't nearer the hole. Did they show him replacing the first time? Did he have a problem with it staying in place?
So, once it was in place (any place, even the wrong one), and he had grounded the club behind the ball and it moved he would get a one stroke penalty and have to replace the ball. Again, if it wouldn't stay where it was, he would have to find the nearest place it would.
As for Dick's other questions, the marker should be place so that it does the minimal amount of damage, but if things are changed Decision 20-1/15.5 says that is ok and you live with any improvement or worsening of the lie. There is a decision (20-1/6.5) that says the marker can be pushed down by anyone including an opponent in match play.