I can copy, this looks like a good find. Intuitively, the matrix should not show in the cellblock, of course. Jit.submatrix (the semi-hack object) does not work on it either, nor does other stuff. Cycling's under the hood technology!
I can understand why this might be a hassle, but what is happening is that once cellblock gets a jit_matrix message, it is then relying on that matrix to maintain it's data structure, regardless of the "physical" connection of a patch cord. jit_deref or deref will indeed remove this connection.
Maybe there is some other attribute we could have to have it not output if it doesn't receive a jit_matrix message again or something, but the intention for cellblock being used in conjunction with jitter matricies is for this reference connection to be made regardless of a patch cord.