Ohh right, I think I might know what's going on ..
If you check my settings, I've checked off for "By field list above". What that does is it makes artist first sort by the filters above it in the list. Checking this off creates a mess where "The Prodigy" gets back under the letter T. Just remember to move your filters up and down in the list so that they're right in the right position, something similar to what I've done in the screenshot.
I'm proud I've stumbled over something I take it people must've struggled with for a while though.
The code for artist and genre is just artist and genre respectively, but the other two are :
- Artist Index : $left($swapprefix($replace(%album artist%,:,!,.,!,0,#,1,#,2,#,3,#,4,#,5,#,6,#,7,#,8, #,9,#)),1)
- Album : $if(%release year%,%release year%,$left(%date%,4)) - %album%
The artist index code lists the first letter unless it's a number. Then it gets sorted under #. Punctuations go under ! although I add those to the code as they appear in my library so there aren't too many specified cases there.