I can't save correctly DDS files, please help

[gigikent]

I want to change a DDS texture in  a game.  The problem is that everytime I save , after modification, the DDS file has a shade of pink, it's like a shadow and is annoying because small objects that i transform tend to look different because at that level even a pixel counts, it distort the form of an object in the texture. I made even this test: I copied a DDS texture , without changing anything and then saved it in its DDS  format. The new texture isn't the same as its origin !!! How can I save correctly the DDS  or is it something wrong with the Paint.net itself ? It drives me nuts this anormality...