The reason I keep on saying .dwg is because in Inventor 2008 there is no more .idw they are only inventor .dwg. Anyways the flat pattern is linked to the .ipt in the drawing and your can only enter a flat pattern in to a drawing if it is the active member in the table. Is there a way to enter a flat pattern in to a drawing with it not being the active member.
Oh wow, I'm sorry, I'm obviously a bit outdated on Inventor... it's been since 2006 since I was active with it. That's kind of strange, but I can see benefits there...
I am sorry, though that I can not help you beyond speculation. My memories are a bit outdated.