This is by design. Creating a RenderTextureDescriptor struct by using the default constructor initializes the struct with zero values, including the flags. This means the struct is not initialized with some flags with the recommended values, including the RenderTextureCreationFlags.AllowVerticalFlip. The documentation warns for this unfortunate behavior of C#: 'Avoid using the default constructor as it does not initialize some flags with the recommended values' (https://docs.unity3d.com/ScriptReference/RenderTextureDescriptor.html). You can solve this by creating the struct using one of the other constructors, such as RenderTextureDescriptor(width, height).