My F1 males that I kept don't show the rear bar, either. I have a couple males from two different spawns and they all have great color and spots, but no bar through the back. They do show the little partial bars on their flanks like their dad, though.
Come to think of it, my females don't really show bars most of the time either. I only see bars on them if they're being chased or harassed by tankmates (usually other severums).