Why do the results of ^ or realpow for special values differ on different operating systems?

[Wafaa Saber abdelhalim]

Upon attempting to get the result of the expressions (+1)^(\pm \infty), (+1)^NaN and NaN^(\pm 0) using Octave3.6.2, I found out that they yield:

a) +1 on operating system Debian 6 with linux kernel 2.6.32-5-686

b) NaN on WindowsXP

c) NaN except (+1)^(+\infty) which yields +1 on Windows7

What would be the source of these differences?