The output frequency of redstone dust connected observers differs depending on the signal strength observed by the first observer.

The below is a 2-clock circuit, which two observers mimic when the first of them observes redstone dust with signal strength 2, 4, 6-8, or 10-15. However when the first observer observes redstone dust with signal strength 1, 3, 5, or 9, since 1.13-pre4 the second observer instead erratically produces 3-tick pulses with 1-tick delay (see lower stripe of redstone repeaters in the images below).

Original, pre-edit description

The circuit below used to drop items from the dropper at a steady rate until it was empty, but since v1.13-pre4 the drop rate is significantly higher when the comparator output signal strength is 1 (i.e. when the dropper inventory contains fewer than 42 items). The drop rate thus changes when the inventory count drops from 42 to 41.

The issue is non-directional and could seem to pertain to the timings of the two observers:

1. The issue goes away when removing the observer pointing into the dropper.
2. The 2-clock signal (...11001100...) produced by the non-dropper-pointing observer remains unchanged as observed by a line of connected 1-tick repeaters.

More generally it appears that the abnormality occurs when the non-dropper-pointing observer observes a 1-strength signal, cause if we move it one block further away from the comparator, the behavior instead shows when the output signal strength is 2: