One reason why DII sell might be this:
DII are mainly the mutual funds in india. When market goes up for a month or so, the mutual fund investors think that its time to take the money out of mutual fund. Thus DII are forced to close their positions in market and liquidate some of the holdings. This "force" is not seen in FII investment... probably diwali might also be the reason why people want their money out of market....
thts why DII chart is a down trend.. while FII chart is UP trend
their might be other strong reasons for DII selling... but this one came to my mind..
any other expalinations???