Question: Kernel connection lost on very simple LinearAlgebra

Hello

I am using Maple 15 on a Macbook Pro, and I was using this simple code

   restart;with(LinearAlgebra):
     P := Matrix(4, 4,    [[1, s, t, 0], [0, 1, s, 0], [0, 0, 1, s], [0, 0, 0, s]]);
DiagonalMatrix(Column(P, 2)).P;

which should be easy but then Maple gives me a pop-up message:

"Kernel connection has been lost.  The kernel returned the following error message:

Execution stopped:Stack limit reached.  You should save this worksheet and restart Maple. Executing commands in maple requires a connection to the maple kernel.

Firewalls have been known to cause problems with kernel connections in Maple.  Please ensure that any firewall software  is configured to allow Maple to create connections to the kernel.  Consult the FAQ for more information."

After that, unless I restart Maple, he won't even do 2+2; anymore.

Is this normal?

Many thanks!