Comment # 1 on bug 1202796 from Michael Andres

Could you please attach the 
   /var/log/zypper.log 
after such a failed attempt. If available also the 
   /var/log/pk_backend_zypp.

zypper sends a dbus request asking PackageKit to quit and release the lock
ASAP. OTOH should PK hold the lock only while performing some action. If you
are constantly blocked by PK, then something broke. The logs should reveal it.