When you lock a ticket it locks the ticket completely to that agent.
It would be helpful if locking could be more granular eg you could lock just replies or the properties box etc
We would like to be able to add agent notes to locked tickets but currently this is not possible.
Official response
Lara Proud
You are now able to add Agent Notes to tickets that have been locked by another agent whilst it is still locked, this change was made to enable even smoother collaboration on tickets without the risk of collision.