*command-line-arguments* is not initialized to a default value
setup-command-line-arguments is registered as an image restore hook, and it initializes the c-l-a variable, but in many situations this hook is not called. e.g. we have our own SBCL specific image save/restore machinery from before UIOP provided its own, or when you just start an SBCL without any image saving and restoration involved.
i think the solution is to call setup-command-line-arguments as the initform of the variable, but i may not be aware of something.
FTR, i've noticed this by upgrading ASDF and the command-line-arguments lib stopped working in our setup and started to use the default values regardless of any args given at the command line.