You could call it a trick, I suppose. It is most likely due to lack of permissions why you can't move the page to another space.
Inside a particular space, you will need:
The 'Add' permission on the page you're moving, and the 'View' permission on the page's parent page. If you're moving the page to a different parent, you need 'View' permission on the new parent.
To move a page into a different space, you also need:
The 'Delete' permission on the space you're moving from, and the 'Add' permission on the space you're moving to.
More info on how to move pages, you will find in Atlassian's documentation for Confluence: https://confluence.atlassian.com/doc/move-and-reorder-pages-146407727.html