That is a known issue with the Actia instrument panel. In July of 09 at the Winnebago Grand National Rally the Workhorse rep said there was a fix for the problem. It requires a firmware re-flash. She offered to have a tech do it to my panel but we were unable to set up a time that worked for both of us.
Since I know that it is not a sign of impending doom I don't really care about it. It has only happened three or four times in ten years and 58,000 miles.
Back in 2005 I got the following info from a Workhorse customer service guy concerning a couple of other issues. I have seen number two often going up steep grades but not number one.
1) Oil pressure can indicate zero and warning buzzer sounds when eng rpm exceeds 4550/4600 rpm. (50 rpm buffer problem)
2) Ave mpg can go to 100 mpg when ave mpg drops below about 4mpg. Data table not large enough.