Usually this rumor is attached to Talia's final episode, "Divided Loyalties" with some fans even claiming that they
saw the kiss in the show's first run and that it was cut later.
These fans are wrong.

*
JMS, Claudia and Andrea are all on record as saying that
no such scene was ever shot for any episode in
any season.
JMS wanted the implications of the Talia/Ivanova relationship to be clear if you were paying attention, but also subtle enough that it didn't become what the show was about. Since he was still in the "slow build-up" phase when Andrea decided to leave, JMS had them spend the night together in the same bed in the course of Talia's last episode without banging the audience over the head with something as obvious as a kiss. But the episode itself is pretty clear about what happened (with Talia reaching over to touch Susan and only then discovering that she's gone, and Talia 2.0's mocking comments to Susan at the end.) Susans' confession that she thought she loved Talia during the modified "rebirth" ceremony was another clear indicator. (I've seen fans try to rationalize this as Susan telling Delenn that she loved Talia "as a friend". But Susan is supposed to be revealing a secret that she has never told anyone else. Why would she keep a
friendship with Talia, even a close one, secret? That certainly wouldn't fit in with the confessions that the other characters made while collecting their Army of Light uniforms.)
Anyway, JMS later stated in a usenet post that the two did indeed have sex when they spent the night together in "Divided Loyalties" and that it was the first time they had. (And that Talia did not detect Susan's latent telepathy because she kept her normal blocks in place - assuming that Susan was a "mundane" and that any telepathic contact during sex would therefore be a violation.)
Regards,
Joe
* When S4 went into the rerun rotation on TNT fans also complained that the scene showing Sheridan and Delenn's wedding had been cut from either "Rising Star" or "The Deconstruction of Falling Stars". Of course, there was no such scene and there never had been. But fans were
adament, describing in detail in TNT message board posts the contents of a scene that they had constructed in their own imaginations and made part of their memory of the episodes. The funny thing was reading 20 or 30 of these messages where none of the details
matched. Similarly fans who understood what was going on in "Divided Loyalties" may have pictured what a Talia/Susan kiss
would have looked like and then incorporated that image into their recollection of the episode. The next time they saw it, with no kiss, they assumed that it had been cut and thus a legend was born.
