Steps to reproduce:
1. Open filechooser dialog (ie. from gimp)
2. Click on the "Modified" column header, to sort by modify time
[a little arrow appears in this header indicating sort column]
3. Go to some sub-directory
[Now we have two sort indicators: one o a "Name" and second on "Modified"
header]

Of course there should be one sort indicator - this previously selected (on
"Modified" column.)

attached screen-shot.