Bug? CUBE map using a LOT of memory

I'm working on a Unity3D app for iOS and run into some memory problems. One of my scenes (the more complex one) uses only 23MB - the other one (the simpler one) up to 120 MB and my app receives memory warnings. Using the profiler I found, that there are two Cube Maps that each take 48 MB. But I do not understand why they take so much memory - they are 1024x1024 and pvrtc 4bpp compressed and unity editor reports them to be 0.7MB

What's going on here? is t$$anonymous$$s a bug in Unity?

I'm using Unity 4.1.3f3 (and cannot upgrade at the moment, since we merge our unity project with an XCode project and updating the unity version last time meant some changes in the Xcode structure that Unity generates and it took quite a w$$anonymous$$le to adapt our project to work with it)