I ran this example in R2014a of MATLAB and I do get -1 at the lower left corner (and upper right)
I created the example in pdetool with the following steps: 1. Create the square. 2. After selecting Boundary Conditions, click on each edge and define r to be the values you list above (y,-y,-x,x). 3. Click the = icon.
What version of MATLAB are you running?
If you want to post your code, I'm happy to take a look.