Swx 2009 Engineering stimulus Package on WinXp Prof. SP3

I'm training myself on swx, and I encountered this strange problem:

I modeled a screw by myself from scratch, including the cosmetic male thread.

Then I inserted it into an assembly, but the position was wrong so I decided to delete it and try to insert it again.

In order to do this, I clicked on the screw and pressed the "del" key on the keyboard, but I actually clicked on the male thread of the screw (my fault), instead of to click over a surface of the solid.

It resulted that when I pressed "del", swx deleted the cosmetic thread and not the part. After this, I saved the assemby and reopened the screw alone: the cosmetic thread did no longer exist on the screw.

To be noted that I was on assembly environment when it happened, and I was not modifing the part in the context.

I'm really new to swx, so I don't know it this is a bug or it works as designed or, last, I didn't understand how swx works.

Regards, Alessandro.