Tried just that line that in AutoCAD, it accepts the path to PDF OK, and then it gets upset at # (being larger than the number of pages)
"There is no # in PDF Enter page number or [?]"
so it moves on and selects the point
"There is no 0,0 in PDF Enter page number or [?]"
Now it selects page 1 (which is the 1 from scale, it will insert page 2 if you change 'scale' to 2)
Now it selects 0 as insertion point (the last point you used?)
Then it pauses asking for scale factor
Then it pauses asking for rotation
Then it inserts the sheet
So the "default back to page 1" is actually it picking up the scale.