I sense that when French speakers see spelling patterns they are either sure of the sound to produce or unsure and thus their natural reaction is to utter the French sound equivalent. This could explain why they can sometimes utter the tense /i/ or /I/ correctly and at other times cannot.
In another example here, the woman uttered /seId/ for /sɛd/. She was unsure, then saw the letters ‘ai’ and naturally said /seId/. So understanding spelling/sound patterns is really important.