Getting strange square root performance.

I'm using the ADAU1451 under Sigma 4.2 to square a couple of signals, add the squares, and then take the square root.  Should be a simple task.  The squaring is no problem at all, I simply drive both inputs of a multiplier like this:

See, the square of 3 is 9, just as I figured it would be.

But here is another static test using the 'basic' square root block. I tried the Precision an the Integer ones with about the same results. This gives me an unexpected number, as if the square root block has gain or something. 

In this example I'd expect to see the number 1, not 16.  Other inputs give correspondingly strange results.  What is it that I don't understand about this? Thanks!