Bellatrix as 'Bella'

[sibel_saya]

No: HPFGUIDX 69075

While rereading OOP, something struck me as rather strange.
In the chapter The Only One He Ever Feared, when Voldemort comes back 
finding Bellatrix and Harry, Voldemort calls Bellatrix 'Bella' twice 
(p716-717 UK Edition).

Now surely this is a sign of affection from Voldemort, something we 
haven't seen before. He calls all the other DEs by their last names 
at the end of GoF, except for Lucius Malfoy, whom he calls Lucius. 
Not only does he call her by her first name but shortens it, 
something we associate with affection. Is this just because she is a 
woman? Or because their relationship may be a bit more advanced 
perhaps (cough cough)?

But also the second time addresses her, he is telling her off, "Be 
quiet, Bella. I shall deal with you in a moment. Do you think I have 
entered the Ministry of Magic to hear your snivelling apologies?" yet 
he still calls her Bella. So what does this mean? I have no idea.
So am I looking in to this too much? Does this mean something or not? 
We know "Voldemort shows just as little mercy to his followers as his 
enemies" after all. So what does this mean?

Thoughts??

Sibel