When user selects multiple tasks and choose a bulk reassignment operation a dialog appears. Under the dialog there's visible the task list and the previously selected tasks are not checked anymore.
When user cancels the dialog (selected wrong one by mistake for example) the tasks are not selected and they need to select again.
It also gives a bad impression, user may think that the selection is wrong (seeing a task they wanted is not checked).
For the other bulk actions this is not happening.