Yes, this is a new feature (app encryption with forward locking) introduced in Android 4.1 (Jelly Bean) which is intended to prevent casual copying of
.apk files. See this blog post for a more detailed description of this feature, with some technical details.
Part of the post text which is most relevant to this question:
A typical forward locked app's mount point now looks like this:
shell@android:/mnt/asec/org.mypackage-1 # ls -l
drwxr-xr-x system system 2012-07-16 15:07 lib
drwx------ root root 1970-01-01 09:00 lost+found
-rw-r----- system u0_a96 1319057 2012-07-16 15:07 pkg.apk
-rw-r--r-- system system 526091 2012-07-16 15:07 res.zip
res.zip holds app resources and is world-readable, while
pkg.apk file which hold the full APK is only readable by the
system and the app's dedicated user (
So a normal app like SaveAPK cannot read
.apk files of forward locked apps in JB (but app resources are still world-readable, therefore apps which contain icon sets and themes for other apps will still work properly).
However, this protection is effective only in the locked-down state of Android as shipped by device manufacturers. If you have root, you can still access
.apk files of all applications installed on your device and do whatever you want with them. The only problem for you is that some backup apps you have used previously will no longer work, and you need to find a working replacement (now a backup app will need to use root access in order to backup all