As a motorcyclist, there has been discussion of the issues that may arise when winter-blend fuels meet summer-blend fuels in the gas tank. Some people seem to have difficulties when they pull their bike from winter storage despite proper storage technique and the blame has been placed on the mixing of fuels (one has ethanol as an additive, the other used to have MTBE, but maybe has something different these days.) In a motorcycles tank, one may be mixing the different blends at 1 to 4 versus 1 to 10 or more when you fill up in a car, leading to more reaction between the two in the motorcycle.
My thought was that Kirsten may be experiencing something similar when they switch fuels due to the much higher proportion of ethanol in the E85. Maybe?