Thank you for your post.
This issue has come up several times on the forum, and it appears to be a timing issue. See the following forum threads to see if any of the solutions work:
Another user on the FMForum site updated Java to fix the issue.
Thank you. It might be the same issue, but the work around I mentioned earlier works for us on every server where we had this issue (and there are quite many, on various configurations (Mac, Windows, different versions of FileMaker Server versions…) and takes only a second to apply.
I would like to point out that wether or not the fact that this work around works is incidental, it is highly abnormal that selecting an item in a Pro dialog without committing changes something in the file that makes the HTML admin console see a difference.