I thought I could customize the width of the grey navigation column when I saw the double arrow cursor (similar to the columns in a Mac Finder window, or changing the width of a browser window), but when I drag and release the menu snaps into two possible states; open or minified.
There are two different levels of interaction here; the finger cursor click and the double arrow dragging. But they both do the same thing - open or minify. From a user's perspective; if I can control the edge of a container by dragging it with with my mouse, I'd like it to remain at the width it is released at.
Possible solution: Perhaps remove the double arrow cursor and dragging functionality so that there is only one way a user can interact with the menu (by clicking). Keep it simple :)