display – Preview bug on BigSur

after installing BigSur Update from Catalina I have encountered some problems with preview:

I use multiple desktop (on the same screen) and then, when pdf is opened, when I switch to the other desktop, preview remains opened also in the other one.

I thing it’s a bug only for Preview because other apps stay in the desktop in which they have been opened.
The only way to bypass is to open pdfs with Safari or Acrobat.

Any helps? thanks in advance