To reproduce:
1. Create an object with a Timeline.
2. Open Timeline window.
3. Zoom in timeline as much as possible.
4. Use right mouse button to select a small region.

Expected result: Timeline is not zoomed in more than it's available to zoom in with scroll wheel.
Actual result: Timeline is zoomed in more. (as much as was possible to zoom in in 2017.3.0b6 and before)

Reproducible: 2017.3.0b7, 2017.3.0b10, 2018.1.0a5
Not Reproducible: 2017.3.0b6 (it was possible to zoom in more)

Note: Also, when it becomes zoomed in more, it does not zoom out nicely, after some scrolling it just jumps back to it's "zoom in" limit.