Hi, In the first biplot both component 1 and component 2 (the columns of your matrix) are in the same direction and magnitude.
In the second example, biplot() makes the largest magnitude coefficient (element) in each column positive. That is the sign convention. So the -6 in the second column becomes positive and all the other elements in the 2nd column change sign to be negative.
That does not affect the interpretation, which demonstrates that x(end,1) and x(end,2) differ from the relationship between x(1:end-1,1) and x(1:end-1,2)