Steps to reproduce:

1. Create new project.
2. Create particle system. (Any other object works really)
3. Create animator and assign it to particle system.
4. Create animation.
5. Click add property in Animation window, click fast between options.

Expected result: Selection selects where you click.
Actual result: Selection sometimes fails to select when clicking fast, selection reverts back to last (GIF).

Reproduced on: 5.4.0b20, 5.3.4f1, 5.2.4f1