hgwebdir backward compatibility issue in 1.5.x

[TK Soh]

Recently I updated our app server to Mercurial 1.5, the very afternoon
many users complained that they were getting RepoError when browsing
their index pages published via hgwebdir.cgi script in their cgi-bin.
Just to put out the fire quickly, I reverted back to 1.4.3.

Is there's any issue in 1.5 on this aspect? I don't see anything in
the release notes. Maybe I missed it somehow.