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Two things to check to get grid mode working right:
First, iTunes wants to sort by "Title" first, then by "Artist", so make sure those field are filled in. For TV Shows, under artist you can just do "Battlestar Galactica", but make sure EVERY EPISODE has this filled in. Even 1 ep missing this tag can blow grid view.
Third, is the YEAR field. Make sure there are ALL filled out for EVERY episode. I use the year a given show aired (say "1997", "1998" and so on), but in a pinch you could just use "1" for season 1, "2" for season 2 and so on.
That should fix your grid view assuming you haven't messed with iTunes default "View -> Sort TV Shows" setting and your "Sort" tags.
Trust me, I spent about 3 months (on and off) trying to figure this out but I finally got it.