Unable to clear color buffers other than 0

[j-o]

ClearStage uses RenderInterface::obtainFBO(size_t index, AbstractRenderTarget * renderTarget) to get an FBO for a specific attachment. This overload does not set draw buffers and neither does the clear stage. This works for color buffer 0, as the default value for the draw buffers array is [GL_COLOR_ATTACHMENT0, GL_NONE, GL_NONE, ...] (see https://computergraphics.stackexchange.com/a/3937), but fails for any additional color buffer.

Who should be responsible for seting the draw buffers?