Solved mystery behind 41-byte-backups

- obviously apps really *can* refuse to be backed-up via ADB
- updated `known_issues` accordingly

Author: IzzySoft

doc/known_issues.md

@@ -1,11 +1,13 @@
 # Known Issues
 
 ## Some apps simply don't want to be backed up via ADB
-At least on my P880 I've encountered several apps which seem to simply refuse
+In my tests I've encountered several apps which seem to simply refuse
 being backed up via ADB. In those cases, backups result in a 41 byte file (which
 is just the backup file header). So watch out for those, and see to have them
 backed up by other means; as *Adebar* here is no more than a "front-end" to the
-`adb backup` command, I don't see what it could fix here.
+`adb backup` command, I don't see what it could fix here. As the example of
+[DavDroid](https://github.com/rfc2822/davdroid) shows, this is rather to be
+fixed on the corresponding Android app's end.
 
 Apps which I found having this issue include the following:
 
@@ -14,7 +16,7 @@ Apps which I found having this issue include the following:
   - SuperSU
 * installed as user apps:
   - AppMonster Pro
-  - DavDroid
+  - DavDroid (pre-0.6.4; fixed [on DavDroid's end](https://github.com/rfc2822/davdroid/releases/tag/v0.6.4))
   - JuiceSSH
   - MobilityMap
   - WakeLockDetector