Double integral fail, works on TI

[roadrunner]

Could it be because

∫(e^((-x)*y)/(x^2-y^2),y)

returns

(Ei(-x^2-x*y)*(e^x^2)^2-Ei(x^2-x*y))/(2*x*e^x^2)

replacing y with x or -x results in Ei(0) which equals -infinity?