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The Synchronise with Debtor and/or Creditor check box is a system setting that persists against the currently open contact form only. If you have the check box ticked, then scroll forward to other contacts, the setting will continue to apply to any contact in the currently open form. It’s not linked to the contact record. It’s a setting that applies to the form, not the contact record, and not the logged in user.
The setting is off by default so if you open contacts in a new form it will now appear off.
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