To reproduce:
1. Download the Cache Server from http://docs.unity3d.com/Documentation/Manual/AssetCacheServer.html and start it.
2. Open a project that has a bunch of assets (i.e Angry Bots)
3. Go to Unity -> Preferences -> Cache Server
4. Set the 'IP Address' field to 'localhost'
5. In the project view, right-click and 'Reimport All'
6. Open the terminal
7. Navigate to the Assets folder of the project
8. Run: find . -exec touch {} \;
9. Open Unity window
10. Observe the cache server receiving requests for "cache/00/<Long GUID>-00000000000000000"
11. Observe the cache server PUTing cached elements that do not match "cache/00/<Long GUID>-00000000000000000", instead it PUTs the file with a correct HASH instead of 00000000000000. It tries a PUT when the file already exists, and every file it has unnecessarily reimported already exists in the cache.