AssetDatabase consistency issues across operating systems

Earlier in our project, one person imported models and for the materials used backslashes. While backslashes are fine on Mac OSX, this creates issues when one tries to open the project in Windows. So I went through and removed all backslashes in asset names in the entire project from within Unity. However, when I try to open the project in Windows, I keep getting the same errors on the same files.

I'm assuming the asset database still has these invalid-on-windows filenames in it still and is trying to generate the files again.

Am I correct? What is going on here? In addition, Unity should not allow asset names that don't work on the other OSes it supports.

This sounds like unity is regenerating the materials based on the names of the materials in the imported model. Those probably have backslashes. Remove them from there instead. We should indeed not allow assets whose names are not supported on all platforms.