I just discovered that when you choose "Allow management of content types" (in the Advanced Settings of Document Library Settings), you lose the "change column ordering" function. This setting also puts all the columns into alphabetical order, which is bad from a usability standpoint. The columns revert to your chosen order when you un-check the "Allow management of content types" option, but then you lose your custom content types. I can't find a workaround and couldn't turn up anything searching Microsoft Support or the web in general. Hopefully, update to follow.