In case you didn't make the connection; that Keeper in the jar is why Sheridan & Delenn are on Centauri Prime in the WWE/ItB flash-forwards, and why Delenn says "our son is safe!" David got Keepered and held hostage, because the Drakh still held a grudge.
It's been a while since I've seen this episode but I vaguely recall Londo trying to subtly signal to them that something is "off." Though Londo being Londo, him seeming "off" is just "Londo on a Tuesday."
Either that or Delenn's shadow detector implant was triggered by the proximity of the keeper, as it did when Morden showed up.