I'm not sure if this really to be considered a bug, or a bug per se.

The issue is only visible when setting GL_LINEAR as the texture's min/mag filtering parameter. Doing the interpolatin by hand in the shader seems to help, but I can't get something decent without sacrificing performance at the moment (cubic interpolation takes its toll when it comes). In my test software, where the new smoke drawing code comes from, although it is using the same texture parameters (plus mipmaping), it does not have any such banding issue. The only difference is that I am using OpenGL 3.3, but I doubt it has anything to do here.

@Mike Erwin (merwin), @Brecht Van Lommel (brecht) do you guys have any ideas how to approach this, or is it some weird OpenGL filtering issue fixed in later versions?

I am closing this because it is basically invalid with 2.8 development.