A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
I just ran through all the options for this same issue (i.e., when originally opening the file, even from another desktop, the file would open in the original desktop that the app was open on) For instance, Excel was originally open on Desktop A, and even though the file navigation occurred on Desktop B, the file still opened in the app on Desktop A)
Here's what I was able to work around: When you click on the task view navigation, you can right click on the app/file you want to move to another desktop. Instead of selecting either of the "show this" prompts (which will move the entire app or just duplicate across desktops), hover over the "move to" selection option. This will allow you to move that one task window to another desktop and will maintain the separation.
This worked with both Excel and PowerPoint which have been my biggest headaches so far. Seems like it should work on others as well if running into the same issue.