Yeah, sounds important.
Workaround: Run Lix with the replay filename as single argument. On Windows: Drag-and-drop the replay onto the Lix executable.
I'll have to see how hard this is to fit onto the existing architecture. Internally, for the file browsers, Lix uses a virtual file system that merges the user's writeable tree (./local/share/lix/ or equivalent Windows) with the Lix installation's read-only tree. But on self-contained Lix, there's only one tree (in the working directory) and you'll never notice any such tree merging. On Windows, Lix is always self-contained because I don't support Windows package managers.
Filenames (Lix's internal filename handling) are already either pointing into that virtual filesystem (they look up from the few fixed roots) or absolute (lookup ignores the roots and hopes that the OS fetches something useful). Virtual filesystem filenames come from the browsers. Absolute filenames come from the command-line arguments.
What we want for this bug: Somehow browsing with absolute filenames in a way that doesn't break too much existing browser UI.
-- Simon