Blender keeps messing up the texture paths?

Hello everyone, I am a Blender user of 4 years and I came across this weird issue recently that never really happened before. Everytime I assign the texture, when I open Blender file again or even copy the model to another .blend file, the path changes and the texture is blank, means it needs to be reassigned, eg. it originally is C:/User/Documents/texture/image.jpg and when I open I find something like tmp/textures/image.jpg and I need to manually go to C:/User/Documents/texture/ and select image.jpg again.
Any suggestions?
this is happening on multiple computers, running Blender 2.69 on 64 bit Mac OS