Superstitions are all false, take unlucky 13 for example, 13 is deemed unlucky because it used to be deemed lucky for some and because of this it got twisted to mean unlucky for all the others, people just make things up as they go along.
Putting brollys up inside - of course that's going to bring bad luck, you are bound to know something over or break something lugging that big thing around in a confined space - even outside they are unlucky, I've been poked in the head/eye more than once by someone carrying a brolly.