When you 'wake up' your phone is in its partial awake state, instead of asleep, your old lock bar may come up.
LockBot and Lock 2.0 activate when the phone goes from SLEEP to PARTIAL AWAKE/AWAKE. If your phone is already PARTIAL AWAKE when you wake it up, your stock HTC lock bar may well be there.
The other lock screens are something of a band-aid over the HTC lock screen. Without Root Access, the HTC lock screen is still there, but Lockbot and Lock 2.0 sort of bypass the HTC one, but can only do so (again, without root access) when the phone is coming from being all the way ASLEEP.
Sometimes, the phone will become partially awake before you press the WAKE/SLEEP/OFF/END button, and then when you think you 'wake' it up, it was really already awake, and BOOM, stock htc lock screen instead of lock 2.0 or lockbot.
That does stink though. I can imagine trying to show off my phone to my friends, and have this happen. I stopped trying, I just use the stock lock screen. Once again, with root access, this can be changed. It's a fact of life until then, unless 2.1 does things differently.