Locking means you have checked-out something that needs to be checked in.
In other words, when you are viewing plugin parameters, you should leave this area by clicking on the cancel icon.
If you leave in any other way, you get a locked plugin.
To unlock, you can just do a global Joomla check-in call.
Regarding session problem, beat has posted known issue and fix or you can wait for next RC (currently in testing).