These are preferred issues which holders can exchange for a predetermined number of the company's common-stock shares. This exchange may occur at any time the investor chooses, regardless of the market price of the common stock. It is a one-way deal; one cannot convert the common stock back to preferred stock. A variant of this is the anti-dilutive convertible preferred recently made popular by investment banker Stan Medley who structured several variants of these preferred for some forty plus public companies.

You need to know the exact terms of preference. There are big differnces between different issues.