iso changing by itself on d40x

[ryssmarr]

I have a d40x and though I'm shooting on manual and setting the iso to ISO 100 when I check my exif data the iso is not set on 100 it changes by itself sometimes it 125 and sometimes its 250 and so on. I'm pretty sure that's not supposed to happen on manual mode. I DO NOT HAVE THE ISO SET ON AUTO. help