Not importing iptc terms into specified taxonomy

I've set the vocabulary in the Image Metadata Settings to "Image Metadata."

I have an "Image" content type and created a field called field_iptc_keywords, set the field type to "Term Reference", and the widget to "Metadata from image." Additionally, I've set the vocabulary to "Image Metadata" in the field settings (not sure if that matters.)

When I save an Image content type with keywords, keywords that already exists as a taxonomy term for another vocabulary are saved to that taxonomy. Keywords with no existing term in a vocabulary are saved to the "Image Metadata" vocabulary.

Example, the image has the following keywords in iptc. green, blue, orange, black. If "blue" is already a term in the "Tags" vocabulary, then the "blue" keyword gets associated with that term. If "green", "orange", and "black" do not have terms in any vocabulary, they are added and associated (correctly) to the "Image Metadata" vocabulary.