I have only tried my I-40s in the video mode on one occaision, I pretty much got the same result you did. It did continue to take stills after the video seemed to be full. The only possible answer would be to use a larger sd card. I use 1gb cards but I think the Moultries can use up to a 4gb. So I would suggest that. Hope this is your answer.
Blessings.....Pastorjim