There is strange behavior with the TAdvListbox component.
If I click on an entry that is only half visible, the entry sometimes jumps up and the next entry is marked.
Sometimes everything stays and the correct entry is marked.
Internally in TAdvListBox, the standard VCL TCheckListBox is used. We could see this behavior also in TCheckListBox, so the issue is in the standard VCL TCheckListBox.
This will need to be reported to Embarcadero.