Why have the member IDs changed?

Can anybody explain, why after the update I'm now #1056.
When I registered, I was 881 and proud of it !
Why have I been declassed ?

I believe the amount of "registered" members is the number you see at the base of the forum page as opposed to the number of people that have applied to be a member but not yet validated their account; so when you joined, the number you saw was the number of validated members and not your actual application for membership number.

Aha !

So, you've saved me once more. Thanks!

As Slackmack said, the number shown on the main page is the total number of members with an activated account.

Account IDs are incremented every time a new account is created. The same number is never reused, even if the account is deleted or is discarded because the user fails to validate. This is why the IDs are higher than the total number.