And if it is standing up all of Shabbat, like a stoller cover is - thus being a true אוהל עראי.
Someone needs to ask Ovadya Yosef if it is okay to carry an umbrella that has been opened before Shabbat in an area that has an eruv.
How many unbrellas could you balance that way? I would guess even if accidentally you own the one which can, it will still be a מראית עין untill they would be more common.
(And as much as I am not a pupil of Rav Ovadya Yosef, and do not usually follow his teaching - he is more than just another of your friends, and it would behoove you to acknowledge it. You needn't add שליט"א, but some acknowledgement would be appropraite. And weren't you complaining a couple of months ago on how some belittled Rav Lichtenstein?)