There's some sort of non-linear scrolling acceleration happening in the creative inventory when scrolling very fast. To reproduce with mouseWheelSensitivity:1.0, do the following in 1.12.2 and 18w21a and compare how far down you scroll:

1. Open the creative inventory on the "building blocks" tab
2. Flick the scroll wheel quickly once

In 18w21a, it jumps to the end, but in 1.12.2 it only gets partway.

In case no difference is observable with your finger motion, try the same experiment on the search results tab with an empty search query.