As usual this was the programmers fault
. Tytus quickly posted a false accusation against festo before we had a chance to diagnose. The problem was we were sending either fwd=1 or rev=1 instead of fwd=1 and fwd=0. In other words we sent it on/open both directions, but you have to turn these either on or off. Sorry Mr. Festo - we love your solenoids!