Aliases are not recognized within calculated fields. Therefore, if this trick wanted to be used, another calculated field that assigned each member a new name will allow you to get the mid to work accordingly. Hope this helps!
Tracy, that explains things a bit, though why screen shot 1 & 3 aren't the same (even though the formula is the same) is a bit odd. But since I now can't recreate that same behavior, who knows. FYI: I didn't put the aliases on the dimension [Store Name] -- as you pointed out aliases don't survive calculated fields (just like number formatting ). Instead I put the aliases on the calculated field/filter itself. What's rather interesting (curious) is that using MID() to trim the dimension, effect the calculation aliases.
Not that any of this matters, because what I really want is the ability to manually sort the order quick-filter options are displayed (you hearin' this Jun?).