How to reproduce:
1. Open the user-submitted project
2. In the Project Window select "testanim" and expand it
3. Select the "Test Take 001" animation and hit Ctrl+D to get animation out from the fbx asset
4. Right-click the newly created animation asset and check its size in the file explorer
5. Open the Animation Window and repeat steps 2-4
6. Observe the difference in sizes

Expected result: Animation window shouldn't affect the fbx asset and both.anim assets have the same file size
Actual result: When the Animation window is opened, the .anim files sizes pulled from the fbx asset almost triple

Reproduced in: 2018.3.0a11, 2018.2.7f1, 2018.1.9f2, 2017.4.11f1