When using the NGG plugin to insert an image in a post
-click add image in add media tools
-from popup select nextGenGallery
-from dropdown select gallery
-from listing select show (anything other than first image in gallery)
-select options
-click insert image
No matter which image is selected for insert, the first image in the gallery is the one that is inserted.
Note; only IE6 seems to have this issue, so probably a js compatibility issue