Dont kid yourself regarding whether common or preferreds do or dont affect the SP. Shares are shares. In this case a dividend is being paid to preferreds. That money comes out of the same coffers that value the common shares causing the company to have less cash.
The market itself (all those smarter than you and I) does not care what any particular shares classes are named. Shares are shares and they are accounted for in the SP, which is 'market value' after all, regardless of what anyone else thinks.
"Bad news is an investors best friend. Its lets you buy a slice of America's future at a marked-down price."