They are counted as part of banks' capital, and prudential regulations often require pension funds to hold a minimum share of their assets in government securities.
Under the scheme, if a bank's capital falls below 8% of its risk assets, the recommended minimum for institutions doing business abroad, the state would either lend money to it, buy its shares - or nationalize it.
If Mr. Market trashes your investments in a sudden panic, your margin debts may be "called, " forcing you to sell some of your assets to sustain the minimum account values you committed to under the terms of the loan.