On YT they mentioned it too on her demo but I think it's just the way triphones were recorded, without any details...
I wonder if they meant like, you want her to say "desu", "shita", "kokoro" and such and you have... Well, I don't know how to describe it, but you know, when the vowel is half-pronounced due to accentuation and such, as those words sound respectively as "dess", "shta" and "kokro"... Even though it can be achieved with any Japanese voicebank shortening the "su", "shi", "ko" etc...
Or if it was just to make the result even smoother...