- Import the attached UNET - LowLevel.jpg file
- Set Tecture type to Sprite and Sprite Mode to Multiple
- In the Sprite Editor select Grid Slicing and slice the image
- Press Apply

Result:
!GetPersistentManager().IsStreamLoaded(metaDataPath)
UnityEditor.AssetDatabase:StopAssetEditing()
UnityEditor.SpriteEditorWindow:DoTextureReimport(String) (at C:/clones/uGUI/Editor/Mono/SpriteEditor/SpriteEditorWindow.cs:1045)

Asset import did not unload metadata path. This will leak memory. File a bug with repro steps please.
UnityEditor.AssetDatabase:StopAssetEditing()
UnityEditor.SpriteEditorWindow:DoTextureReimport(String) (at C:/clones/uGUI/Editor/Mono/SpriteEditor/SpriteEditorWindow.cs:1045)

This is a regression compared to Unity 4.6.0b5. The whole process of slicing and applying the changes also takes much, much longer than before (probably caused by the memory leak)