The cue to stand up can be an internal urge or a command by someone else. Processing the sensation of standing may take 10 or 15 seconds, and then they are ready to assist with a pivot transfer. They are aware of the position of their head and can hold it up while standing or sitting, but they may not be able to sustain their attention to locking their knees long enough to continue to stand up.
Trunk control for balance may have the same problem with sustained attention. If so, it is not dependable, and they will require support during transfers and chairs with arm and back supports.