I have a FC980M and I had never noticed this, but yes, doing the same that you do in your video, my spacebar behaves very similar. I wouldn't consider this a defect. I always hit the spacebar with my thumb on the left part of it, and it feels ok. By, the way, I have it flipped. Have you tried it? It's so much more comfortable to use! When I received my keyboard I spent also some days worrying about the feel of the long keys, trying to find out if they felt more or less mushy or more or less scratchy. Cherry stabs make long keys behave a bit different from the rest. And keep in mind that these stabs are clipped, which mean they are better than most of the stock Cherry stabs that most of keyboards have. Moreover, remember that spacebars are the week point of many highend keyboards. Look, for instance, many Filco users complain that their spacebars rattle a lot, simply by touching it with your finger. Another example, the expensive Topre keyboards also have spacebars that sound and behave very differently from the rest of the keys (and to put things worse, they are made of abs, unlike the rest of the keys, which means they will get shiny after some months of use. Others have keycap sets with warped spacebars, because they are difficult to produce correctly with PBT plastic. So, don't worry so much and and enjoy your brand new keyboard.
