At what stage did I say I was using a "shandie"? lol
I have asked the factory about this on a previous occasion, they stated that its fine to top up on either fuel provided one or the other is the majority in the tank. Also I was told that it was to stop a trend that was developing, of people mixing 91ulp with avgas! had nothing to do with 98+.
When I say fuel up at other locations its a case of leaving 'home base' burning down to practical and topping up with the other until I get home.
To be clear the engine is out of warranty!