What's the Difference Between a Short and a Long?

If two conditionally marked clauses occur together without an intervening conjunction, the sentence expresses counterfactual. What I'm interested in is there are two successive usages of the short or ab-al. There might be some... One might be assimilated into it. But there's nothing in this grammar that tells us that, I don't think. It just says that the imperative can be used in any person, which strikes me as something that's slightly unnatural.