Okay I will have to backtrack a little on this item.
In v7.5.2 at least when you delete a member in the control panel you do have a option to preserve the name of the poster.
Here is a sample with a member name of iaei.
Warning: Deleting a member can not be undone.
1. Do not delete this member.
2.Delete member and do not alter posts. Ownership will be set to Anonymous with an Anonymous name of: iaei.
3.Delete member and delete all posts. If there are any replies to a post by this member, they will be attached to the post's parent. If the user's post is a topic, the entire topic will be deleted.
So if you select the 2nd option it will preserve the user name.
It works in 7.5.2
Hardly ever use this feature but if it was in v7.1. It probably was a bug to not work correctly.
So since you can't upgrade right now Sirdude's suggestion is probably the best fix for now.
