I wonder if they were testing with the paid, commercial version or the free evaluation version of LispWorks, which has significant restrictions.

Most people playing around with this will be using sbcl though. It's overwhelmingly the most popular free common lisp system.

It sounds like it would preclude doing any actual work with LispWorks, yes. But maybe someone at Harlequin will take interest and fix whatever the LispWorks bug is, or in the unlikely case that it's a CL-Forth bug, propose a fix. (It could be a CL-Forth bug, because Common Lisp allows you to turn off safety.) It doesn't preclude doing any actual work with CL-Forth, though, because you can use better Common Lisps.

You can use CCL

Use SBCL.