IIRC the sometimes problem was that the center of the bullet would blow thru and leave the rest stuck in the bbl.
The center was very thin on some as the cavity was very deep.
Most of the 38 W/Cs bought were sweged and were very soft lead. They were fine for what they were intended for,,light target loads.
When trying to pump them up into something like a +P , the reletively thin center of the very soft alloy bullet blasted through.
That occured whether they were loaded upside down or not.
The problem never caught much attension until the craze of upside-down loading them started to catch on.
It was supposed to be an easy way to make your M36 or D/Sp into a real stopper.
Hard cast alloy HBWC bullets don't have the tendency to blow through, but the word was out,,and most shied away from using the loading procedure no matter which W/C.
Much better bullets & powder choices available now than there was in the early 60's when I first recall a lot of talk about it in the gun rags.. I'm sure there were those loading the HBWC backwards before that too.