You're right, this is a misread from the voice actors side and/or not being checked properly by moderators.
Since it is just an extra letter at the beginning of a word this could probably be fixed adequately using an audio editor.
Definitly "ilin ĉien" on the audio -- still there three years later. If we want things fixed at the advanced levels, more DUO users have to actually use the advanced levels.
I was wondering this too. But when I typed out: Lia hundo sekvas sin ĉien I realized that the dog would be following itself.
Which would make a great video, but might not be fun for the dog.
Ĉien kien Marry iris, Marry iris, Marry iris, Ĉien kien Marry iris la ŝafeto certe sekvis.