There is a significant difference between moving a block of activities with the mouse versus with the arrow keys (or Gestural Interface window).
Suggested Practice
When a block is moved with the mouse, the starting position of each activity is moved by the same distance. The starting dates for all activities are then recalculated from the new starting positions.
When the block is moved with the arrow keys (or Gestural Interface window), the starting date of each activity is moved by the specified number of working days in the calendar of the activity.
For example, imagine two activities assigned different calendars that start and finish on the same dates.
If both “Sample Calendar Activity” and “Sample US Activity” are selected and dragged with the mouse until the starting date of the first activity is 11/8 the following is the result:
However, if the move is performed using the arrow key four times the result is:
The difference occurs because the “Sample Calendar Activity” is moved by 4 calendar days, while “Sample US Activity” is moved by 4 working days (equivalent to 6 calendar days because the starting point of each activity moves past a weekend).
In short, when using the arrow keys, all objects are moved by working days (in the calendar of the object). This means that objects assigned calendars with more non-working days will move ‘faster’ than objects assigned calendars with fewer non-working days.
Because of these differences, users should generally use the mouse for block move operations and only use the arrow keys (or gestural) when working with single activities.