Editing PDF metadata doesn't work

The fields I want to edit are "Author" and "Title".
At first I edited those fields (in Dopus) for 2 PDFs created with Indesign (fields were empty before). Both times, one of the edited fields was empty again when checking the dialog in Dopus after editing. Then I edited those fields again and it stayed in there.
It doesn't appear in the PDF view though, neither in Sumatra PDF nor in Acrobat Pro.
Then, I tried editing a PDF document that was created with FrameMaker and where the Author and Title fields have been filled in using Acrobat Pro before. After editing a field, it saved and displayed correctly in Dopus, but Acrobat and Sumatra still display the value that was there before.

Next, I created an empty pdf document with Indesign and entered text into Author and Title using Dopus. When opening it in Acrobat, the fields were empty. I entered text again using Acrobat.
When clicking OK, Acrobat displayed the error "Dictionary Keys must be direct name objects" and didn't save the changes. (Edit: I tried the same thing again now with a different PDF that was edited by Dopus, and now Acrobat displays "Undeterminated string" as error instead.)
I tried it repeatedly, and after a 3 or 4 tries it didn't display the error message again and saved the changes. (I attached the last file below.)
MetadataTestFile.zip (2.0 KB)

Adobe might go its own mysterious ways when it comes to editing fields and storing metadata. PrintMeta is a handy tool for monitoring operations like this and determining which fields can be edited in Opus.

https://resource.dopus.com/t/printmeta-write-metadata-to-text-files/42786

Yes, Adobe just loves to make things complicated for everyone else.
I saved your tool as a bookmark, it looks useful for analyzing large amounts of files at the same time.

I just edited this same file again with Dopus and now Acrobat displayed the change made in Dopus this time as well as the change I made before that! How come?