Reproduction steps:

• Drag and drop the attached `sample.m4a` file into Picard
• Observe the presence of a Record Label field with the value `TEST LABEL`
• Right click the Record Label field and choose Remove
• Press the Save button in the menu bar
• Observe the Record Label field has disappeared as expected
• Press Remove in the menu bar to remove the file from the main panel
• Drag and drop the file back into Picard
• Observe the Record Label field is now back, with the `TEST LABEL` value again