I have two that are doing the opposite. Stems with leaves on top, but no buds. Too bad we're so far away from each other that we can't get them together, and show them the error of their ways. LOL
I'm assuming that the plant has bloomed normally before? I've heard people blame such strange occurrances on chemicals such as insecticides and fungicides, especially the systemics. I've also heard Superthrive blamed for strange things. Since you have more than one plant doing the same thing, I'd say it's not just a random occurrance. So maybe a chemical could do it?