Hi, gromit.
Detrius may be correct, i.e. there may be directory corruption. Disk Warrior would certainly be the best tool to repair this if that is the case. You can also determine if Directory Corruption is the cause by running Step 1 from my
Resolving Disk, Permission, and Cache Corruption FAQ. If any irreparable problems are found, Disk Warrior would probably do the trick.
However, there can be other potential causes for this:
1. Corrupted Finder preferences. See my
Finder Issues? How to delete its preferences FAQ.
2. One or more corrupted .DS_Store files in the folders in question. These files contain info used by Finder to display the folder window.
(1) Download the donationware application
Cocktail.
(2) Launch Cocktail.
(3) Select the Files icon in the Cocktail toolbar.
(4) Select the DS Store tab.
(5) Select the Chose button.
(6) In the resulting window navigate to and select the affected disk, volume, or folder. For example, you might want to select your Home folder.
(7) Select OK in the resulting confirmation window.
Cocktail displays a sheet indicating when it has completed the task.