Huge File Sizes

I do beer signs for a living.  Sometimes I like to import other coreldraw files into my current work to take designs off of them, such as a curve or a portion of text.   I then delete the unused parts.   The problem is that whenever I do this, it makes the save file huge!  

You can test this.  Open an empty coreldraw file.  Drag a few .cdr's into it.  Delete everything you imported. Save the empty file.  It will be the size of all those .cdr's combined!

Is this a bug or something I can fix?