I understand that keeping them moving would be bad for performance.
But shouldn't that be not so much of an issue, once items on a belt are optimized in 0.16?

In that case, I'd expect the belt to move, since there's nothing that SHOULD be blocking it. The item on the input-belt would stay on that ...

See here:
https://image.prntscr.com/image/BOWn6jzOSrCI36nzEKguvQ.png

While the northern belt was loading science packs on the outer lane I noticed that it pushed items on the belt a bit behind, if there was a gap somewhere.
Upon closing the last gap, the items stopped flowing complete.

No Mods ...