In all Unity versions as of this post, Unity's Package Manager window is broken. If you click the Update button to download an updated version of an Asset Store package, it will keep the old version in the Asset Store download cache folder instead of the newly-downloaded version -- even though the window says that it has downloaded the updated version. So when you then click Update, it will import the old version instead of the new.
The only solution is to delete the old package from the cache folder first, then refresh the Package Manager window before downloading.
The cache folder is located here:
- Windows: [user]\AppData\Roaming\Unity\Asset Store 5.x
- Mac: ~/Library/Unity/Asset Store-5.x