Nothing went wrong and the TMA-13M crew (Alexander Gerst (ESA), Maxim Suraev (Roscosmos) and Reid Wiseman (NASA)) are by now onboard the ISS. The way it looked to me (watched it live) was that the camera's aperture ratio wasn't adjusted fast enough with the fast changing incident light, so the frames were overexposed as the Soyuz-FG rocket engines were ignited.
A combination of rocket's own exhaust, reflected light from the deflected exhaust plume (Soyuz rockets launched from Baikonur Cosmodrome are placed over a quarry-like "hole in the ground", for lack of a better word) additionally illuminating the site, and camera's F-Stop in the same or similar position as prior to the engine ignition with dark night's background and the whole site only illuminated by a set of reflector lights, meant that the live transmission camera produced an overexposed image during liftoff. I could swear that the camera's position was also slightly more towards the "quarry" this time, more in the way of the deflected exhaust plume, but I can't confirm it.
So I'd have to say it just appeared that there was more flame than it should have been, and as @LocalFluff mentioned in his answer, no anomalies were reported.