Well, I've done quit a bit of research on this and it is well known, though there isn't much conclusive data on it. Wm. C. Davis mentions it with Bullseye in his reduced loads article from 25+ years ago,
I have a lot of respect for Davis' writing and would be interested in reading what he has to say on the subject.
The only real info in that thread is that Hercules and H.P.White labs were unable to cause a detonation or explosion with light loads of fast burning powder. The rest is all unsupported opinions.
Detonations caused by light charges of
slow burning powder in
large cases is another matter entirely.
On your first paragraph, do you have any references for that phenomenon? It's not at all intuitive to me that you'd have enough pressure to launch the 148 grain wadcutter through the barrel and down range, but not push the case back, especially with the firing pin pushing on the primer.
I'm sorry that I can't explain this part any better, except to say that I have experienced it in a couple of guns myself. The results of firing leave the primer protruding noticeably, but without the slightest sign of high pressure. This only happens with guns that have a lot of excess headspace and or springy actions, which result in excess headspace.
The best example that I have seen is my 1893 Marlin lever action rifle in .32-40 caliber. With a load of 7 grs. Unique and a 170gr cast bullet, the primers will back out far enough that the cases will not fit back into a standard shellholder. This is a very mild load and there is not the slightest sign, ever, of excess pressure. When the gun is fired with a normal load, the primers remain flush with the case head. There is probably not enough difference between Bullseye in a pistol and Unique in a rifle to make this experience invalid as a point of reference.
I also had a Colt revolver in .38S&W caliber that exhibited the same behavior with light loads. I no longer have the gun, but clearly remember grinding a groove in the top of the shellholder to allow the cases with high primers to be decapped. The gun was , by appearance, in very good condition and the high primers did not happen with full loads.
I think that the reason that the guys that shoot the wax bullets open their primer pockets is to keep this from happening. It might be interesting to check it out.
Since Bullseye powder has been used for light to very light loads for many decades, I firmly believe that there would be warnings in every manual printed for the last 50 years, if this was a real problem. Smattern fact, I doubt that the powder would even continue to be sold.
There is a fair amount of info on the net about "cat sneeze" loads that might offer you some reassurance that light loads of fast powder are not too dangerous.
BTW, try a google search for "primers backing out", there are quite a few folks that think that it happens mostly with light loads and excessive hadspace, if there are not other signs of high pressure.