It seems like the move has less range than it did before too. The only time I see it really put to use is when Nakamura uses it to as a combo ender in the corner on rare occasion to create space for Secret Garden oki.
It's when you use FD (Faultless Defense) to cancel your dash and go into FD to prevent the sliding recovery animation after a dash(also known as Dash Brake). The dash brake has a stronger effect when you do crouch FD as well (you slide forward a bit from the dash momentum when you do standing FD).
4gamer's Millia Wiki Character Page
Contains frame data, descriptions of her moves' properties and uses as well as a basic combo video.
Here's the full frame data table.
EDIT: Updated most of her character wiki page with the numbers here.
EDIT: Updated the character page with more of the numbers(recovery and active frames) and images.
2014/7/5 Mikado 3on3
Satou (Millia) vs Taka (Slayer) (Satou puts one of those crazy Chroming Rose combos in action in training mode after the match)
Satou (Millia) vs Mugen (Sol)
Tsubu (Bedman) vs JUN (Millia)
U-Zen (I-No) vs Toruso (Millia)
Samitto (Chipp) vs Toruso (Millia)
Tsubu (Bedman) vs Toruso (Millia)
2014/5/3 Mikado (A fairly strong Millia)
Shuri (Millia) vs Tsubu (Bedman)
Shuri (Millia) vs Roi (Sol)
Shuri (Millia) vs Tsubu (Bedman) 2
Shuri (Millia) vs Tsubu (Bedman) 3
Shuri (Millia) vs Tsubu (Bedman) 4
Shuri (Millia) vs Roi (Sol) 2
Shuri (Millia) vs NOB (Sol)
So I noticed in one of Daiji's matches against an I-No player that he used S-Tandem and YRC'd it at the same time I-No got into hitstun from it. It happens at around 8:34 in one of the videos Ronove uploaded: http://youtu.be/1BlBoXod-d8?t=8m34s
A glitch perhaps where the game didn't recognize I-No in hitstun during maybe the first frame? Maybe Daiji YRC'd a frame beforehand?