Sirius' Knowledge of House Elves

[grindieloe]

No: HPFGUIDX 82271

This is a trivial observation, but Sirius was under the impression 
that house elves were bound to their masters' houses.  Harry informs 
him that in fact they were not, and that they could leave if they 
wanted to since Dobby did visit Harry at Privet Drive.  

In CoS, Lucius Malfoy visits Hogwarts to talk with Dumbledore and 
Dobby is actually with him.  I realize this was necessary for 
the "freeing of Dobby" scene.  However, Malfoy obviously is aware 
that house elves can certainly leave their houses.

Why then is Sirius not aware of this fact?  Is it because he was away 
from Grimmauld Place for so long and hadn't actually been surrounded 
by a house elf for many years?  

Or is Sirius under the impression that house elves cannot leave 
unless accompanied by their masters?  This would explain the CoS 
scene with Malfoy & Dobby, since Dobby was in the company of his 
master.

What do you guys think of this?

grindieloe