I've had lots of issues with this and i've never gotten a clear answer, there's been workarounds which i'm doing now but for the sake of knowledge...
why does
Sprite.texture = SubTexture
work fine assigning a texture to a sprite
but...
BaseTexture.draw(SubTexture,texture_position)
Sprite.texture = BaseTexture
show a blank image?
As far as i can tell this is how the draw() function is supposed to work, drawing one thing inside another.