In the Babylon 5 season 2 episode "A Race Through Dark Places", Bester comes to Babylon 5 to hunt rogue telepaths. The rogues kidnap Talia Winters and convince her to help them. At the end of the episode she and the rogue telepaths manage to create a false memory in Bester. They make him believe she betrayed the rogues and the two of them (Talia and Bester) shot all of them.
However, later in the season, in the episode Divided Loyalties, we learn that Talia Winters has been a spy for the Psy Corps, which secretly planted an alternate personality in her brain.
Since her true personality was loyal to the Psy Corps, why would she help the rogue telepaths trick Bester? And even if she wasn't aware of the alternate personality spying for the corps, how could she help the rogues without that alternate personality finding a way to report to the corps about the rogue telepaths still being alive?