Playing Second Wave on my Fed, I went through all the delegates and tasks (including optionals), and did my part in the conference. All was expected...
Until the moment I started trying to convince Ambassador S'tass. One click started the negotiations, then IMMEDIATELY afterward, the cutscene with the Jem'Hadar ships started, mostly intact except for the wormhole FX (but that might have still been loading).
After it ended, the game acted like this hadn't happened, like I was still embroiled in negotiations (right where I left it). Immediately after I convinced them all, the cutscene played again, in it's proper place (and with all FX), though the motions of the Jem'Hadar soldier killing the Admiral + S'tass killing him had already been played, so they did not repeat.
Everything else seemed to be in order. Edit: Seems to be fairly consistent.