Question

When I am manually creating or editing a record, I check the Disable Duplicate Check checkbox. But when I click Save, the checkbox is automatically unchecked again.

Answer

Note that from DC version 3.362 onward, the Disable Duplicate Check checkbox does not need to be shown on the page layout anymore in order to override the blocking of saving records that have duplicates. If you still have the checkbox displayed on the page layout, it will always behave as if it is ticked for those that can view the checkbox.

When saving records that have duplicates detected is disabled in general, a user with field access (at least Read access) to the Disable Duplicate Check field will always be able to save records that have duplicates detected. Read more in DC Entry.

For earlier versions:

This behavior is by design. Duplicate Check can prevent duplicates from being manually inserted/updated by hard-blocking the "save." The Disable Duplicate Check checkbox is only for bypassing the prevention temporarily, so that users can save the record by setting the field value to 'True'. After saving/updating the record, the checkbox is set to 'False' again automatically.

Note:
If you want to exclude certain records from being analyzed by Duplicate Check at all times, please use the object filter. Read more about the object filter at the bottom of this article.