fluids not moving past inline outlets in series, to next inline outlet

This is not a bug, and easy to explain. First your last picture. A line with branches to the inputs of your valves. This works fine, because the line is solid, and everything else is going away from there.

Now the picture with not flowing gas. 

This is passthrough through the inputs of the valves. Now a certain rule applies. A passthrough is always counted as exit node, until its full, and only then it counts as throughput. But because gas could flow in both directions from every input to any other input, the system stops to work, because the path is not clear anymore. 

You should always avoid possible flow between to ports in both directions.