When an inserter is dropping items into a splitter it seems that normal, fast and express belts cannot be saturated.
This is different from version 1.1.
This problem doesn't occur when using turbo splitters.
Steps to reproduce:
Build a chest and a bulk
I also made a video showcasing this issue.
It can be found here: https://www.youtube.com/watch?v=3iVuNEElaxc.