Copy/paste in Inkscape
By default, if you copy and paste a vector object in Inkscape, it converts it to a pixellated object (!).
To fix this, you can either use the Duplicate command (
ctrl-D) or change the behavior of the clipboard in X11. To do the latter, in the Preferences of the X11 program, go to the Pasteboard tab, and uncheck the box that says "Update Pasteboard when CLIPBOARD changes". This will prevent copying and pasting from X11 to OSX, but you probably didn't want that pixel object anyway!
Further instructions are on the official Inkscape page.