Yes, it is an expected behaviour.
Perhaps I'm missing something stupid, but this behaviour of the preview Synchronized bugs me:
Suppose that I select two subdirectories dir1/ dir2/ from my local dir and try to synchronize to the remote. Suppose that dir1/ exist in the remote (but it's empty), dir2/ does not exist. Then, the preview window shows me all the files and subdirectories of dir1/ and lets me choose what to upload. Instead, it doesn't let me choose inside dir2/ : it's all or not for a new directory. Is this expected behaviour? I cannot understand why.