Questions about Poppy's Steadfast Presence with Shen's Shadow Dash

So I just recently had a game against Poppy playing as Shen and have a few questions in regards to her (E) Steadfast Presence.

I understand that Shen's (E) Shadow Dash is a "Dash" and he would be knocked down if used while Poppy's (E) is up when he is in her range and it does not matter if he is dashing to or away from her while in the area.

What I am confused about is how Poppy's (E) knock down still works after Shen already taunted her. Right after I dash and the taunt begins, I am suddenly knocked down and she is no longer taunted.. It seems like her (E) is a Clarity against taunts while being taunted.

I am guessing the 1.5 sec taunt is still considered the "Dash" part as it is part of the same ability but that does not make any sense. He technically already dashed and is now taunting them (no longer dashing towards them) technically two steps in his ability. Am I thinking about Shen's (E) wrong or is something actually wrong with Poppy's (E) or something that was not mentioned? Well in short, that cost me the lane and a death or two but it did not allow me to actually be able to do anything but take more damage.

Also, another thing I'm wondering. Would flash be considered a "Dash"? I tried doing that twice (once when a Lee Sin came in to gank) and failed both times in Poppy's (E). Also Lee Sin was not Lvl 6 yet so he did not have his knock back either.

If someone could clarify this for me that would be great.