Reproduction steps:
1) Open attached project
2) Open scene "TestScene" and
3) Select "TestAnimation" game object
4) In the Animation Tab select "SourceAnimation" in the clips list
5) Select all the properties, and copy them to the clipboard with ctrl + C
6) Select the "TargetAnimation" clip
7) Deselect everything and try to paste with ctrl + V
--- Properties will not be pasted

Regression introduced in version 5.4