In the edited post if you click on "Last edited by Javaphile" you will be taken to a history of all changes made to the post. There you will see that the only difference from the original post to the one you see now is the formatting of the video link. The old format no longer worked (No link nor video appeared in the post.) so I changed the formatting of the video link so that people could see the video. If you need further proof scroll down through the thread and you will see where some people, notably those using an ipad, could not see a video in the original post. In post #9 you will see where another user posted the video link using a different format so everyone could view it. Note that it is the identical video link that appears in the now 'fixed'/edited post.
Now onto the expansion issue.
Your other misquote/misattribution is "Rather it is sucked up into the S/Screen during the vacuum effect just prior to first water flow.
Which this video does not concur with your inference". What I said, in addition to the above 2 quotes, was "The screen imprint comes when the shot is stopped and the pressure is relieved when the 3-way valve opens which results in a negative pressure in the portafilter sucking the puck up against the screen." (Note bolding added by me.)
post #24 in the Clear naked portafilter thread? In shot after shot it clearly shows that the puck does not expand until the shot is stopped and the pressure is relieved.
Now as to the sucking/expansion question there are several issues to be addressed. Depending on the machine being used the puck's behavior will be different.
The machine being used in the long (9:24) video releases the pressure very gradually when the 3-way valve is opened at the end of the shot to relieve the pressure. With a gradual relieving of the pressure the best description of the puck's behavior is that it expands, by quite a bit as shown in that video, which it can do as it has a huge overhead. If it had been dosed to the proper level (i.e. Very close to but not touching the screen.) it would clearly have expanded into the screen.
When used on a machine where there is a near instant reduction of the pressure when the 3-way valve relieves the pressure at the end of the shot the entire puck is sucked upward into the screen before it has a chance to expand. (There used to be several other videos using a different machine where this effect was shown but I no longer seem then linked/shown on Vimeo. As I recall they were done by the person who did the first, shorter, video in the Clear naked portafilter thread.)
No matter which machine is used and whether it is via just expansion (A slow reduction of the pressure.), or sucking (A very rapid reduction of the pressure.), or a combination of the two the screen imprint does occur but not until after the shot has ended.
As to your argument that the puck is too heavy to be sucked, up a few grams difference in weight means absolutely nothing when dealing with 9 or 10 bars of pressure.
Now, there is a scenario where the above behavior will be different as the forces involved are different. This would be on a machine where there is no 3-way valve or other mechanism to relieve the pressure at the end of the shot. On those machines you have to wait for the pressure to be relieved via exhausting through the puck. (If you don't wait and force the portafilter off you will have a quite powerful explosion sending scalding water/steam and coffee grounds all over you and your kitchen.) I suspect on one of these systems you may see a slight expansion of the puck. How much will depend on how fast the pressure is relieved through the puck. On some machines you may even see a sucking action if the pressure relieves quickly enough and the brewing head cools off enough to create a negative pressure differential between the inside of the grouphead and the outside atmosphere. On other machines there may be no expansion nor sucking behavior displayed as the puck may dry out as the pressure is relieved making it too dry to expand.
Java "Did I miss anything?" phile