Owned a house where this had been done on chipboard. Bfore wwe bought it they had installed heating and the plumber cut a piece of floor out along the wall leaving the wall sitting on chipboard cantilevered out about 12" from and parallel to the next joist - it dropped 3/4".
Took the wall down and replaced it with a stud.
It may be common but is a short cut, I believe the block wall should be stood on 2 lenths of 3x2.
It's not common these days but certainly was in the past. Most likely it was to do with sound insulation more than anything else. I once got caught out by third floor walls in a 180 yr old building that were off floorboards with nothing below. I assumed they were stud walls but they turned out to be brick.
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