QListWidget problem on Mac, not on linux/windows

I have attached a minimal project that will illustrate the problem, which is as follows:

The main window features a tab widget with only one tab.
Inside the tab widget are a list widget on the left and a tree widget on the right.

If you first start the app and click the 'open USB link' button, after about 5 seconds, you will see some timestamps appear in the list widget. If you then click on the tree widget on the right (which will get the focus on Mac) and then click the 'Get Directory' button, the list widget will be cleared and new timestamps should appear. This doesn't happen, *unless* you select the list widget on the left!

This only happens on Mac (Qt SDK Mac opensource 2009.04), not on linux or windows.

If I get rid of the tab widget and place the list widget and tree widget directly on the main window, the problem doesn't happen.

Any ideas?