When you create a new Business Partner, the numbering of the Business Partner id is not in sequence, i.e. some of the IDs are missing.
Reproducing the Issue
Go to Business Partner Data work center
Under Common tasks, select New Business partner
After saving, you found that the Business Partner ID is not in sequence
The Business Partner ID is drawn during the Finalize (Step before saving) phase, afterwards still checks are performed (i.e. email address or postal code correct).
If the check is failing (due to some error message while saving) and the user exits the process, the ID is nevertheless Burned.
The same cause applies for External ID if the ID is not in sequence.
This is expected system behavior. The system works as designed.
Missing Business Partner ID, Number not in Sequence, Business Partner ID sequence , KBA , SRD-MD-BP , Business Partner , Problem