It probably checks the ui name table to see if something with the same UI name exists instead of constantly looping through the datablock group unless it keeps track of brick sizes of all brick datablocks.
I'm guessing it doesn't though, so if the UI names for the bricks are different, it'll probably have a load error.
edit:
Actually there'd be no logical way I can think of that it would keep track of the brick sizes so it has to use UI names.