I got a more compact case for this issue, by changing the in1 and in2 to
ex in1 = reader("t^2/(3*m^2-t*m^2)/2");
ex in2 = reader("-(m^(-2)*(-3+t)^(-1)*t^2/2)");
sometimes we get the output:
in1-in2 = 0
diff = 0
while, for some other times, we get the output:
in1-in2 = 0
diff = 96*log(1/48)
it seems that the sign of the log term has been changed.
Best regards!
Feng