Pan drop.
The pantographs installed on the legacy network Flexities are "smart", and are capable of lowering themselves if they detect any situation or motion that could cause damage to either the overhead or themselves.
They are arguably too sensitive however. Early on, a pan drop was considered a major fault and required the car to be removed from service immediately. I guess that they've finally realised that there is no damage to the pantographs when this happens, and so the car (in most cases) can switch to the pole and have its pantograph inspected later.
Dan