iMovie 11 9.0.9 cannot adjust clip times to fraction of a second

I am now using a new mac 13 inch with retina dispay, OS mountain lion, and iMovie 11 9.0.9. I used to be able to adjust the duration of a clip to within a fraction of a second. For example: if I set transitions to 2 secs., then set clip duration to 3 secs. the clip actually plays for 5 secs. (using 1 sec. from each bounding transition). Fine. If I changed the clip duration to 3.5 secs. accordingly the duration would last for 5.5 secs. Just what I want. This no longer works for me. After entering 3.5 secs I get 5.05 secs or some such nonsense. I showed this to a creative person at a onetoone and he told me I could never do that. mmmmm.