Unable to change borders of a GUITexture in a straightforward way

Hello,

I'm making the classical energy bar rendering thing using to GUITextures :

• One texture at the back represents the back of the bar and never changes

• One texture is partly drawn on top of the first one, depending on how much energy is available.

I'm therefore trying to draw only one part of my top texture. I managed to get it working by manipulating the pixelInsets and borders properties of GUITexture. So everything seems fine here, EXCEPT I have to write it in a weird way apparently :

         // (fgGUITex is my front GUITexture object 
         // on which I set the pixelInset property previously).

         // For some mysterious reason, the borders are not modified if I write this :
         //fgGUITex.border.left = (int) (ratio * fgTexW);
         
         // ... this howether works as expected !?
         RectOffset ro = fgGUITex.border;
         ro.left = (int) (ratio * fgTexW);
         fgGUITex.border = ro;

Could someone tell me why my first (commented out) instruction does not do the same as the following lines ? Am I doing something wrong here ? My guess is that I might have ran into some evil C# property that does more than acessing its field without notice ... ?