The Notification scheme has the entries
|Current Assignee, Reporter
If User 1 assigns a single issue to User 2, User 2 gets a notification email.
But if User 1 uses the bulk edit feature from the navigator to assign several issues to User 2, he does not get a notification email.
It seems that the bulk change is considered only an issue update, not a change assignee.
I think this is a bug ar at least a problematic inconsistency. The assignee should get an email regardless of whether it has been triggered by a single action or by a bulk change. My customer relies on the emails being sent to the respective developers. If emails do not arrive, or if the send email notification feature is unreliable, it looks as if the developers are lazy and this is a severe problem.
This issue affects probably also earlier releases than 3.5, but I don't have test environments available right now.