Just gave this a try and it does seem to work, both stable 4.0 and the latest (4.1.0+300).
I did notice a few things, though:
Is the info (year+creator) you added actually saved? Had some problems before I figured out that it will not save the year/creator tag when still in that formula field (“edit mode” if you like). You need to be outside of it (tab will do).
I do not have the $(CATEGORY 0(creator)) tag. I used the $(CREATOR) tag to test.
If the data cannot be found there’s not message and the (empty) IPTC field is not created
I checked in both GIMP and XnView to see if the IPTC data was added (both showed the same, correct info).