System Information
Operating system: Windows 10, Version 1809 (OS Build 17763.615)
Graphics card: GeForce GTX 1050ti

Blender Version
Broken: 2.80
Worked: (optional)

Short description of error

I'm animating a scene, and as I made it longer and longer, I extended the end frame further and further. However, this final time, I extended it from frame ~1290 to ~1850, as shown, and the lighter gray part of the timeline, which indicates what parts can be keyframed etc, has not moved on. The dark gray part, which is used to show the area outside the start and end frames, is able to be keyframed, and when I play the animation, it continues on into this.

Exact steps for others to reproduce the error

From the file below, in which I've deleted everything not needed, simply take a look at the Timeline. You should see the 'visual' end of the animation is around 1290ish, while in actual fact, it is 1850ish.