Blocks in assembly layout sketch: referencing dimensions in configurations

Hi everyone,

I am trying to use a block in an assembly layout sketch, starting with a very simple task. I set up a rectangle, centered on the sketch origin, dimensioned it, and made a block. For some reason, I can't reference the block's dimensions when I create a new configuration. When the same entities are created in a regular sketch, the dimensions update when you change configurations. As soon as the rectangle becomes a block, it no longer works. Any ideas?

SolidworksAssemblies