Well woldn't that still be TTI since Crono and Lucca remember Marle and still exist in 600 AD because Leene wasn't yet killed? Just like with the example of Crono's mother and the black omen. But dont' get me wrong, I still think its strange that they are even able to travel in time once the reason to travel in time is eliminated (and the rest of the Guardian Line.)
Wait, I just read that over. I'm so convinced that its a plothole now....maybe. Why would the effect of Leene's capture have consequences on the future so suddenly? That would be like...you traveling to 65,000,000 (enough 0s?) to get the dreamstone and all of a sudden be holding the mended Masamune....wouldn't it? I'm confused I think, but I'll stick with plothole.