There was a previous bug about this that has been marked complete, however it still occurs.
  1. Create a task
  2. Create 15-20 sub-tasks
  3. Link the tasks in a linear fashion
  4. Enable "rescheduling of dependencies" and "hide weekends" in Gantt view
  5. begin moving tasks lower in the dependency chain
  6. Observe the tasks later in the chain do not move the same number of days as the start of the chain.