[Orgmode] Turning on column view marks buffer "modified"

[Wanrong Lin]

If I turn on column view for the whole buffer by pressing "C-c C-x C-c" 
at the top of the buffer (blank area), the buffer would be marked 
"modified". But if I do it just on a subtree, everything is normal. Does 
anybody see the same thing? thanks.

Wanrong