If using the "slide to unlock" option on the lockscreen it is possible to pull down the notification bar while the phone is locked.
If using any of the other lock screens (i.e. face, pin, pattern or password) you cannot pull down the notification bar.
I am calling this a bug because it defeats the purpose of a lock screen. This is causing me to accidentally pull down the lock screen and click on the various notifications that are in the drop down and start them up and sometimes interact with whatever app happens to come up, all while the phone is in my pocket.
A lock screen should be made to prevent pocket dialing the phone, not facilitate it.
If this is a UI "feature" it should be disabled, or at the very least opted out of via a settings item.