version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-06 23:23, hash: aa003c73245f, type: Release
build date: 2019-06-07, 00:08:40
platform: Linux

How to reproduce:

1. Open the file and inspect the animation
2. Select all the keyframes
3. Enter edit mode
4. With multiframe edit enabled, select all the strokes for all the frames of one of the two fishes
5. Using "Arrange Strokes", try to switch the fishes so the red fish passes in front of the blue fish

The operator only works on the stroke for the current frame.