I bought and planted a 12 pack of geraniums this year. They are a cheery and giving plant. I just wish they came back. I, too have noticed this but don't know the cause. I just snip the flower stalks off when they get ratty looking, even if there's a couple of buds left unopened. I like to pot up a couple in the fall before the first freeze and overwinter them inside as houseplants. I know that doesn't answer your question, but I hate to see a post go unanswered!