OSX Applications folder window has become 'unsortable' OSX 10.8.2 (Mountain Lion) 

My Applications folder has recently become unsortable when it's open in Finder. That is, all the various headers of each column in the Applications window are flat white and clicking on any of them has no effect. I'm not sure what's caused it; whatever caused it, it's not something I've done deliberately.

Normally, at least one column header is in the computer's highlight colour, to signify that's the one that's controlling how the window's files are sorted. In this case, none of the headers are in colour, and clicking on any of them has no effect on the sort within the window. Only the Applications window is affected, all the other Finder windows work normally.

Thinks I've checked: 
• The folder that encloses the Applications folder sorts normally, and folders inside the Applications window sort normally when opened.
• A new folder created in the Applications folder, when opened, works normally.
• All the applications inside the applications folder launch normally.

In Get Info, the Applications folder is not being shared and nor is it locked (the Locked option is greyed out, however). The Sharing &amp; Permissions table shows that the System and Admin (which is me) can each Read &amp; Write to the folder, while Everyone is read only. There's nothing obviously out of its proper setting in Get Info (although I don't know if the grey'd Locked setting is normal for the apps folder; it is live in other folders.

Opening the Applications folder in a new, virgin account on the same computer shows the same problem.

At the moment, the files in the folder are sorted in reverse order (z to a), which is annoying but I can limp along with it like that.

Do you have any suggestions for how I might fix the folder so that it sorts properly?

Things I've tried:

• In the Get Info window, changing Everyone to Read &amp; Write temporarily has no effect on the issue.

• Changing Admin to Read Only temporarily, and then back to Read &amp; Write, has no effect on the issue at either stage.
Finder has had separate arrange by and sort by modes since 10.7. That usually happens when arrange by is set to something other than none.

The pop-up button on the toolbar always changes the arrange by mode, but View > Arrange By turns to Sort By when you hold option, and for example ⌃⌥⌘6 sorts by size.