Sorry but i am not sure to understand : it seem your description, expected and actual results below are all contradictory.
! is the duplicate operator : it must find all records that have exactly the same string on a specific field
During this find, all the field's content must be identical. This find is not word-based.
This operator can be followed by a string to be more specific : only this duplicate string will be found.
I did a test with a brand new file using FileMaker 12.0v5 on a Mac OS X 10.8.5 and couldn't reproduce any issue.
Thank you to provide further clarifications.