Someone can correct me if I'm wrong, but let's take a simple example. Suppose company A has 100 shares outstanding valued at $1 a piece. So company A is worth $100.
If company A releases 100 more shares of stock onto the market, assuming their value stays constant, the shares are now all worth 0.50/share. So companyA gets 0.5*100 dollars to spend on things, and the people owning hte original 100 shares are angry b/c their shares got devalued. Releasing new shares is called "dilution". In general, dilution is viewed as a sign of weakness & usually the stock takes a hit after dilution; e.g., the company is releasing stock to raise money b/c they're in trouble. In this case, the holders of the RMBS convertible will convert them to shares if the price goes over 26.80, meaning that the net # of shares will increase (even though RMBS didn't release them directly).
The real story is more complex than that. Sometimes dilution doesn't signal weakness (HGSI for example, rose after its several dilutions). You can look into that more if you want, but the message is that dilutions aren't always a straight up negative. It's particularly complex with say biomed companies that are simply developing products and don't really have any kind of income.