I can't reproduce this on the Joomla demo site running 4.6.0, and I didn't have this problem before. Now on my 4.6.6 site, if I display custom fields with multi records in a tab, the set of records displays multiple times, along with multiple "Edit multi record" buttons.
If I have one record inserted, it shows once.
If I have two records inserted, they each show twice. (As in example below.)
If I have six records inserted, they each show six times.
I don't have multiple records if I click "Edit multi record", or in "Tab with table" or "Inline" modes. Only the data display in "Tab" mode.
Is this a bug introduced sometime between 4.6.0 and 4.6.6?