I think it's worth pointing out though that even if a behavior is consistent, it doesn't mean it's intended.
Look at the Wavedash, for instance. A correctly inputted air dodge into the ground will consistently result in a slide, but that's still very much a glitch, as it's an example of unintended behavior resulting from sloppy code in the physics engine.
Looking at what we have here, I really doubt that the sing-sliding is intended, so I would call it a bug, even though it's what usually happens in that scenario.
Now if only it were as applicable as Wavedashing...