Steps to reproduce this issue:
1. Import Idle.anim from "UMotion Community - Animation Editor" package on asset store
2. Open Idle.anim in Animation window
3. Open Task Manager, or Activity Monitor
4. Open Curves tab
5. Zoom in/out into keyframes, move through keyframes with the marker
6. Inspect memory usage in TaskManager

Expected result: Memory change is not significant and it gets released when Animation Window is closed.
Actual result: Memory usage increases significantly and is not released after closing Animation window.

Reproducible: 2017.4.18f1, 2018.3.2f1, 2019.1.0a14, 2019.2.0a1