Issue: When you use File > Print to display the Print dialog, which contains both printer settings and print preview, the current window may shift to the background, behind the main Outlook window.
Explanation: Outlook handles Print Preview on the main UI thread. With some printers, depending on variety of factors including but not limited to network latency, printer drivers, and the complexity of the item being rendered, Outlook may appear unresponsive while waiting for the print preview operation to complete. During this time, a feature introduced in Windows Vista, known as Window Ghosting, will take over rendering the Outlook window. Due to issues with how the Window Ghosting feature tracks which window in a process is the current window, occasionally after the print preview operation is complete and Outlook is again responsive, the Windows Manager selects the main Outlook window as the foreground window. This will bring the main window into focus in front of other windows, shifting these other windows, including the window showing the Print view, into the background, behind the main Outlook window.
Action: You can minimize the main Outlook window to bring the Print view back to the foreground.
For more information, see: Windows Ghosting.
To give feedback on this specific issue, see Keep print preview in the foreground when printing on Outlook UserVoice.