Could you try adding a new column by right clicking on the right side of the header bar and choose "Add Column". Choose "Device Properties" and then "Parent Device". If that new column works delete the old one.
You then have to go into the "Configuration" tabs "My settings" and click save at the bottom of the page. This will make sure that when you log back into ipMonitor the column changes will persist.
Hope this helps!
I swear that I had already done exactly what you suggested, but it didn't work.
Second time around, after reading your post, I had success (permanently I hope).
- r -