Ha! That was a good memory jogger for me Boar Fighter.What can i say. YMMV. I do think my S-brush has less bloom than yours (either by manufacturing or because of less use) and it's like a springy broom from hell.
What seems like aeons ago, I sent my beloved S10065 off for a handle upgrade. It looks just great, but it was (accidentally) set 2mm lower than requested. That made it perform just the way you describe yours. I immediately purchased a new S10065 (which fortunately has the standard 55mm loft [vs the 53mm loft on the rehandled one]). I found it quite amazing that a 2mm difference in the knot setting depth made such a radical difference to performance.