[DCP-o-matic] Image sequence… not in sequence ?

Hello, While trying to make one DCP from many still images + many folders containing image sequences, there is an issue : images (from folders) are not displayed in their initial sequence ! I've first thought it was relative to mixed content so I've also tried with only one folder (containing ten images in sequence) but still the same issue. I've then tested with newer version of dcp-o-matic2 (from 2.1.19 → 2.1.21) but not better, on two machines (both Ubuntu 14.04). Maybe problems come from the "pattern" I use to name my files ? In one folder I have 1_01.tif 1_02.tif 1_03.tif and so on… Other folder is 2_01.tif 2_02.tif 2_03.tif and so on… Fourth folder is 4_01.tif 4_02.tif 4_03.tif and so on… You would guess for the sixth and seventh folder ;-) Those sequences are 6 to 18 images serving as transitions/animations between still images. Best regards, Gérald @UnDemiCoeurNoir