I have experienced the same thing, but have found that if I insert the /aba/ immediatedly following www.loc.gov and the rest of the website address (example, http://www.loc.gov/aba/pcc/053/053prop.html)
Then everything works well.
While I really like the new PCC website redesign, the changes have caused a number of broken links in documentation outside of the site.
Is there a rule of thumb I can use to convert previously correct document addresses to their new equivalents?
Head, Special Resources Cataloging / Music Cataloger
University of Maryland