Bunch changes notifications
Whenever you edit property for a bunch of tasks (let say, you change their priority or target version), Redmine sends a single mail notification to registered people for EVERY task, by providing the same information.
For me, it makes much more sense to send a unique email, saying: "the property X has been modified to Y for the following tasks: #1, #2, #3."
This need is evident, for example, when you start a project with no versions, then you create a version and assign all the past tasks to this version. Project administrators will be terribly spammed in such a case.
It shouldn't be that difficult to implement this feature and it could dramatically improve the user experience.