That one isn't actually real.
I played in a community server for months that reverts the Baby Face Blaster back to when it did not have the drain on hit mechanic, and I can definitely tell you that a Scout at the max 500 HU/s does not break his hit boxes. No one has ever complained about it so far.
If anything, all it did was make Scout harder to shoot at unless you have good tracking (or you used the Natascha or switched to Scout). I think it is likely that this was thrown around by players who found Scouts using the BFB annoying (and yes it does get annoying with 4 peak BFB scouts in the other team like it's Boston).