Rob is right on the mark though. With our H36, if we use 91ULP in remote locations, aside from a drop in power, it will often want to run backwards on shutdown. Occasionally at home it exhibits these same symptoms although we use only 98. It looks like our 98 may well have been 91 by the time we used it at times. Goodness knows what the RON of 91 could be after extended storage!
Regards Laurie Hoffman
