OS: Windows 7 - 64bit
When creating a contact sheets and directly switching to "Preview" tab, the preview is empty.
Effect: Irritating user interface.
To reproduce:
1. In XnView browser select multiple image files.
2. Select Create » Contact sheet
3. In dialog "Create contact sheet" select "Preview" tab. (Don't change any values beforehand).
Actual behaviour (bug): Preview tab is displayed. The preview is empty.

Expected behaviour: Preview tab is displayed. The preview shows a preview of the contact sheet.