If you have both block->shutters and whistle->stairs checked off, the whistle doesn't do anything, but the block makes both the shutters and the stairs activate.
2.5 Build 910: Screen Data Bug
try the latest version of Zelda Classic over @ http://shardstorm.com
I checked, and the whistle does do something after a second or two, like it should. However, pushing a block always makes the stairs appear whether or not a screen flag is set or not.
Not a bug!