Meh, the first video, doesn't bother me. You put your knees in the seat, rocked it back and forth, and then popped it with your body weight to get it to collapse.
If the owner is saying it's collapsing during normal use, then it's a problem because of the annoyance and frequent reinstalls necessary. If using noodles in an acceptable alternative (they're not with Chicco, but I think everyone else allows them) with the base in (some manufacturers want the base all the way extended if you need to use additional noodles), then it's a work-around.
Crash scenarios don't worry me in the least with the collapsing base. If pool noodles were used, or if the base collapses, or if nothing of the sort happens, the initial crash phase (downward rotation) won't be affected. On rebound, infant seats and even many convertibles tend to get stuck quite upright, not falling all the way back down flat on the vehicle seat.
I didn't know the D22 allowed the shoulder belt to be wrapped around in European routing. Learned something new.