[Gimp-user] Converting from Indexed to RGB without smoothing the edges

[Alessandro Francesconi <alessandrofrancesconi live it>]

 Don't know if it's a bug or a feature.... but I need an explanation about this behavior:
I have a small icon with an indexed color palette: 
https://cloud.githubusercontent.com/assets/9453825/4901180/1d1cd216-642f-11e4-97db-4f3a76ffdd7c.png
 
You see, the edges of the icon are very sharp... but if I convert it to RGB using the "Change mode" menu, the 
edges become smooth. I don't want this to happen but the "gimp-image-convert-rgb" procedure doesn't take any 
option or parameter for this.

Why does GIMP automatically smooth the edges when changing to RGB?
Thank you!
 
Ale