I created a bunch of animation tracks on a point light object, and then attempted to create an activation track
The track scaled to fill up the track up to frame 3999 and then the timeline zoomed to a per-second scale, and it won't scale down using the scroll anymore.

A second time, this happened after adding a few more animation clips to the timeline.
In both cases, closing the Timeline Window does not fix it, neither shutting down unity and opening the project again.

To reproduce:
open one of the projects attached and observe the timeline on the point light

Tested in :
2017.3 0b10, 2017.30b9, 0b7

Not reproducible in: 2017.2 0f3, 2017.3 0b1, 0b6,