Got the same bug, it is linked to the fact that a cost involved for a quest item apparently does not involve a check to see if you have enough money.
It occured for me because I was low on trias (about 30) but still bought a quest object with a cost of 50 trias involved, when next opening my inventory I realised I had gone into negative trias.
My reaction to this was to sell an object to get back into the positive but the negative tria remained and only got worse as time went on (probably the automated conversion script that acted on) so much so that by the time I had walked to another area I was in the negative for several 100 millions, eventually it became too much for the system and turned into a positive (no drop/ grab of money involved).
While at this stage it isn\'t trully a bother, even if it blocks me from some quests, because I know a DB wipe is on the way the bug is really dangerous because it is not 1.9 billion of Trias as stated before but unlimited money (in other words dropping money will have no effect on the amount you keep, I should know I tried dropping 500000 circles on the floor and the amount I had did not budge).