Activity is cut

Could you give information about priority of the activities ?
It they are all the same, then planning seems normal, priority if given by WBS.

So "Développement PGM transco" is planned =>OK
Then "Modification CL" is planned, but cannot start on the sale day because of predecessor constraint.
Then "tests unitaires pgm transco" is planned => OK
Then "Reprise des fichiers" is planned. And as it has no constraint, it used the availability left on tuesday.

If you want to avoid this behavior, you must allow your task "Modification CL" to start same day as predecessor : set delay to -1 in the dependency definition.