Absolutely wrong. An FFV is just that... FLEXIBLE in the fuel it can run on. I swap back and forth all the time as do many here.
LOL I appreciate you including my experience in that group, Nate. I run varying percentages of ethanol and have not had any trouble with switching back and forth. The only issue that I have with higher percentages of ethanol is during cold starts. It can take mine a bit longer cranking to fire up.