Yesterday's usage is yet to be reset so I am no sure about the software bug thing. It seems that they had manually reset the earlier usage, which they might do in the future as well, but certainly it doesn't seem to have been automated as yet. Another thing to consider is that they have only reset the data usage for connections starting after 10pm, so in cases where I have started a session before 10pm and continued using it past 10pm, I have still been billed for the total volume for that session. Hope MTNL sorts it out soon enough.