Have not tried
I've changed asignee to to myself and:
- There is no modification history for that at all (itemViewDiff).
- There is comment action registered in changes(projViewChanges) on 2007-05-08 at 2:10pm instead of modification or update action (I don't know yet which one should be proper in that case).
Ad.1. Registered change I think.
Ad.2. Modification I think, though it have been made from Update tab.