No. Client Javascripts have been enabled all along. It's definitely the URLInterceptor:
Code:
Debug: Warning: URLInterceptor blocking access to url QUrl("file:///C%3A/Program Files/Sigil/polyfills/MJ/MathJax.js?config=local/SIGIL_EBOOK_MML_SVG")
The only thing I can think of is that we may have to find a way to keep the colon after the drive-letter from being percent-encoded on Windows. I'll try to quickly brute that change and see if it makes a difference.