"A long time since I flew the type, but rapid manual selection can cause the nose to pitch up and this can catch the unawares out. A definite chance of tail strike. The reason, I was told, is that the spoiler panels will come up in sequence normally, with the outboard ones last, to avoid this problem but if manually selected they all come up together. But I could be wrong! I've noticed a similar thing with the 747 Classic, but not the -400."
I can't envisage how the spoiler deployment sequence would vary depending on whether it's initiated manually or automatically. All the "auto" does on a 747 is drive a motor which drives the speedbrake lever mechanism in the cockpit .... from then on, it's basically the same mechanism.
Rgds.
Q