When users select a custom item model in the Editor, the Editor will parse it, find its texture paths, and ask the user to provide the corresponding textures. Finally, it alters the model such that it looks for the textures in the right location.

Unfortunately, when these texture paths contain forbidden characters like : or uppercase characters, these will be copied to the final model, and eventually be rejected by the minecraft client. The Editor should do some renaming to prevent such issues.

This will be fixed in Custom Items 11.5