This is what the xsel man page has to say about the selection "buffer".
There is no X selection buffer. The selection mechanism in X11 is an interclient communication mediated by the X server each time any program wishes to know the selection contents, eg. to perform a middle mouse button paste.
So I'm guessing there probably isn't all that much you can do about it, without looking carefully into the source code or the xlib functions. I can only suggest maybe looking into modifying your commands to copy the primary selection into the secondary or clipboard (y'know, I've never been able to figure out what the secondary is supposed to be for); and hopefully control the timing of when you get it back.