photoshop does not show keywords

[myth5656]

I got an image where some metadata is stored. I want just want to add some keywords, because the image doesn't have any.
After adding them, exiftool shows them on the command line. Photoshop doesn't  show any keyword. When I remove all metadata and add  the same keywords, PhotoShop shows the keywords.

I do not get an error when writing, or opening the image. Are there other attributes which prevent PS to show the keywords?

[Phil Harvey]

I think that reading FAQ number 3 may answer your questions.  The suggestion about MWG tags may be particularly useful.

Let me know if you have any questions after reading this.

- Phil