Comment 1 for bug 1082749

marlin is using nested GtkPaneds for its columns view. When you move the separator one child expand while the other shrink.
In a context of nested paned objects, some child just can't be resized because no space is available for it. This introduce some undesired behaviors.
Due to this behavior and the limitations of gtk (GtkPaned), it's impossible to resize columns other than the firsts ones.
Which is why the columns are not resizeable.

Marking this bug as a long term whislist.