this is an old discussion on the board.  If/when the A's get converted including the dividend arrears, then it would trigger the dividends for the other preferred shares.  When a dividend is paid to one, it must be paid to all.

In the D series prospecutus, if the company goes 'bankrupt', then the dividend arrears become an unsecured claim regardless if it has been declared by the BOD or not and stands with all the other unsecured claims.