Works OK on Eclipse 3.6.1 / Windows XP. On my Macbook Pro (3.6.0 verson of Eclipse. using the 32 bit version I think of the graphics libs (I forget exactly which I loaded), Java 1.6.0 _ 24) it misbehaves but not quite like above.
If I misclick (click on the type number (left column)), it does one of the following:
1) - puts up the dialog telling you to click in the right columns, when you press OK, it puts up 2 more of those boxes, one of which has the OK button highlighted, when you click on that OK, puts up 1 more of those boxes, and when you click OK, it goes away...
2) - puts up the dialog, but doesn't reliably put it in "front" of the Eclipse screen, so you can't click on it.
For (2) - a workaround I found was to close the macbook, making it go to sleep, then open it, and when I log in, it then shows the windows in the right order.
This looks like it might be some kind of timing / race condition issue for Eclipse SWT modal dialogs.
One thing to try is to see if the "Sheets" style works better on a mac - see http://www.eclipse-tips.com/how-to-guides/27-making-good-eclipse-rcp-apps-for-mac (it may be a while before I get time to try this, myself...)