PowerBI altering data in custom column

I've loaded in a dataset from postgres, and I've created a custom column in Power Query, let's call it id, that concatenates two of the table's columns with a hyphen (let's call them employee_id and last_name). After applying these changes, there is one row in my dataset where, in the composite 'id' column, it has mutated the employee_id part for some reason, but the data in the employee_id column itself has remained unchanged. EG, if the employee_id is '123ABC' in the database and the last name is 'Johnson', then the row in question will show the employee_id as '123ABC' but the id will be 'Johnson-123ABc', with the 'c' now lowercase for some reason (the correct id should be 'Johnson-123ABC'). The only Applied Steps that I've taken in the Power Query Editor for this dataset are importing the data and adding the custom column.

I'm wondering why this behavior is happening. As far as I know, it is only happening to one row in the dataset.