How to reproduce:
Have a (sub)root folder (c:\myRoot) with many subfolders (c:\myRoot\sFolder1, c:\myRoot\sFolder2 etc.) and images in it from which at least some of them are not yet 'seen' by XnViewMP.
Perhaps is better for the program to have the default setting to display 4 thumbs for each folder.
Browse the said root folder (c:\myRoot\). The background thread which builds/generates the thumbnails will detect the new folders/items and will start to generate thumbnails.
If the thread isn't finished yet and we'll try to enter in a subfolder (eg. c:\myRoot\foo ) by double-clicking on the folder in the thumbnails pane the program will crash. But for this the user must be quick: double-click on the desired subfolder in the very first few seconds in order to catch the building process. Unfortunately, there are enough users which are very quick...
