Woops - I was thinking Regulus Black, but Typing RAB - just shows you how thoroughly I've embraced this theory.
As for Mundungus - well, the Order seemed uncertain about whether 12 Grimauld would remain unplottable after Sirius' death. Seems to me that if the Order had anything of importance stored there, having Mundungus "Steal" it is a good way to move it. We never SEE him fence the goods.
Re: BIG Spoiler
As for Mundungus - well, the Order seemed uncertain about whether 12 Grimauld would remain unplottable after Sirius' death. Seems to me that if the Order had anything of importance stored there, having Mundungus "Steal" it is a good way to move it. We never SEE him fence the goods.