After several times trying out, we must conclude that there is a bug in factor using the right mouse button. I am using Maple6 on Windows 98. Cklicking in the output and using expand an factor there will be the following session.

> restart;(x^3+3*y^2)*(5*x^2-4*y^3); 3 2 2 3 (x + 3 y ) (5 x - 4 y ) > 5*x^5-4*x^3*y^3+15*y^2*x^2-12*y^5; 5 3 3 2 2 5 5 x - 4 x y + 15 y x - 12 y > x^5-(x^3+3*y^2)*(5*x^2-4*y^3); 5 3 2 2 3 x - (x + 3 y ) (5 x - 4 y )

The commands factor and expand will work without problems but with right mouse button, it is wrong in most of the situations with factor.