Directory Indexes don't work when using file-based basic auth (ShibCompatValidUser is On)

I'm using Shibboleth 2.5.2 on Apache 2.4, on Ubuntu Server 13.10 64 bit.

When I have a directory with an .htaccess file like this:
AuthType Basic
AuthName "Private Area"
AuthUserFile .htpasswd
Require valid-user

It works fine when mod_shib is not enabled, but when mod_shib is enabled and ShibCompatValidUser On, and I try to get a directory listing, I get a 500 error and the following error message:
shib_auth_checker found no per-request structure

When it's a regular file I'm accessing, or the directory contains an index file, it works just fine.

I tried to hack the source code a bit and these are my observations:

• Completely ripping out Shibboleth's valid-user handling code doesn't fix it, so it doesn't seem to have anything to do with that.

• If after line 875 (if (!rc || !rc->sta)) I insert a check whether bCompatValidUser is enabled and return DECLINED, it works, but I have no idea whether this kind of fix is appropriate.

• The error occurs because rc is NULL

• I can always reproduce the error, on different servers, including a clean Ubuntu 13.10 64-bit install on a VM.

For now, I'm using a workaround where I turn on ShibDisable by default, and only turn it off when it's actually necessary.