On Jelly Bean, using FX with root, I noticed duplicate files in /data/app-asec/, e.g.:
com.disney.WMW-1.asec(56,9 MB)com.disney.WMW-2.asec(56,9 MB)
It looks like one is obsolete and consuming almost 60MB.
So I deleted the older ones of the duplicates and also renamed all files to have the suffix -1.
After a reboot, some apps were not working. The launcher showed a “app is not installed” message.
After some more research, I found the file /data/system/packages.xml which contains lines like these:
<package name="com.disney.WMW" codePath="/mnt/asec/com.disney.WMW-2/pkg.apk" resourcePath="/mnt/asec/com.disney.WMW-2/res.zip" nativeLibraryPath="/mnt/asec/com.disney.WMW-2/lib" flags="0" ft="13ab353ea00" it="13484d822a3" ut="13ab3547873" version="16" userId="10214" installer="com.android.vending">So I changed these lines to read com.disney.WMW-1 and after one more reboot, all apps worked again. AND I had 500MB more free space.