Memory leak in symbolic toolbox?

If I try this simple code:

W = 1/100*ones(100); W = sym(W); x = rand(100,1);

for i=1:10000 x = double(W*x); end

which basically does nothing, the memory usage constantly grows, although there is no reason for it. Value x is constant double precision. I don't see this behaviour when the matrix W is not symbolic. It seems like a memory leak in the symbolic toolbox to me. I tried it with Matlab 7.9.0(R2009b) and also latest Matlab 2011b.

Another question is that I noticed that doing a matrix multiplication with symbolic matrix is not a multithreaded operation (in comparison to normal matrix multiplication). Is there some reason for that?