Shada is one of them. As mentioned above, Eight wants an adventure with Romana, so he goes to Gallifrey, grabs her by the hand and says "Let's have tea" then drags her to the Tardis and off they go. Or something like that.
That's a little off. Remembering that Shada was the abandoned story that was never completed in 1979 due to a strike, and then they used some footage from it in The Five Doctors. Years later, the Eighth Doctor gets hit with a strong sense of "unfinished business" drawing him back to Cambridge or wherever Shada was set, because those events were interrupted by The Five Doctors but needed to be completed (who knows, maybe it qualified as a fixed moment in time involving the Doctor). And because Romana and K-9 were involved too, he had to go back and get her. Fortunately for him they weren't stuck in E-Space anymore.
It's a bit messy, but the whole issue is dealt with in just a few minutes and then Douglas Adams' original story kicks in.