Comment 8 for bug 519577

I've looked at the source and it looks like the /var/lib/oss4 path and the OSSVARDIR var were introduced in the debian/patches/cmd.patch and debian/patches/os_cmd.patch patches. Also extra files were edited:

$ find |xargs grep var

./debian/patches/cmd.patch:+#define DEFAULT_OSSLIBDIR "/var/lib/oss4"
./debian/patches/cmd.patch:+/var/lib/oss4/legacy_devices
./debian/patches/cmd.patch:+ if (stat ("/var/lib/oss4", &st) != -1) /* Use /var/lib/oss4/mixer.save */
./debian/patches/cmd.patch:+ strcpy (name, "/var/lib/oss4/mixer.save");
./debian/patches/cmd.patch:+ strcpy (ossetcdir, "/var/lib/oss4");
./debian/patches/cmd.patch:+settings into /var/lib/oss4/mixer.save or $OSSVARDIR/mixer.save file.
./debian/patches/cmd.patch:+OSSVARDIR is decided by reading /etc/oss.conf, and defaults to /var/lib/oss4.
./debian/patches/cmd.patch:+/var/lib/oss4/mixer.save
./debian/patches/cmd.patch:+/var/lib/oss4/dspdevs.map
./debian/patches/cmd.patch:+/var/lib/oss4/applist.conf
./debian/control: This package contains various utilities for configuring
./debian/oss4-base.init:OSSVARDIR=/var/lib/oss4
./debian/m-a/rules:# load generic variable handling
./debian/m-a/rules:# following variables:
./debian/oss.conf:OSSVARDIR=/var/lib/oss4
./debian/oss4-base.dirs:var/lib/oss

Fixing the path /var/lib/oss4 to its original value, /usr/lib/oss4 as pointed out by Jason could make the trick, I've tried to change it by myself but unfortunately I couldn't rebuild the package after making the changes. Maybe someone who has previous experience with quilt/cdbs could fix it.