When Jack Sparrow is in the English prison, notice when the Black Pearl shells the city, it punctures a hole in the prison wall through which Jack's prison inmates escape. Specifically, take note of how a small portion of that hole overlaps Jack's cell. Later, when Will Turner visits Jack, the hole is no longer there. Given that he visited the following day, it's highly unlikely that such a trivial hole had been patched, since there was no longer anyone in the adjoining cell.