[...]
Am I right? And if so, is there a way around this, as in merging the two screens to have both xlib and draw commands show at the same time?[...]

Hey, hey! Nice. Thanks yet again, Kerm. Slowly but surely, I am getting better.

Hm, it sounds like xLib draws directly to the screen... I haven't used xLib, so there may be an option to draw to the buffer.

Explanation: (this'll also explain my above comment)
In the TI-83+ series, the LCD is not mapped to a RAM area, so the screen has to be updated separately from the area that contains its contents. In BASIC, when you execute a drawing command, the buffer (that's what this area is called) is updated to reflect the command, and then the entire buffer is copied to the LCD.
What's happening here is that xLib is drawing directly to the LCD, which means when you execute a normal BASIC drawing command, the buffer's contents overwrite what's on the screen and hasn't been saved to the buffer. The resolution to this would be to use the versions of the commands that draw to the buffer, and then execute the command to copy the buffer to the LCD (this has to be done manually in xLib, and this is mainly for reasons of speed. It is much slower to do something like "draw sprite, update LCD, repeat" than "draw sprite, draw sprite... update LCD")

...Are you using ULCD = 0 or 1 for the last argument?

Sorry for the delay, had to run to the store.

Tried it, same result, but quicker flicker (since it draws all at once, eh?).

Also tried other methods, like saving the xlib stuff to a pic, but the pic turns out blank, again showing it is separate from the graph buffer.