They do that in Wisconsin too... Pure Maple Syrup and Lagered Beer 50/50 with 87 octane.
*Update* Just had 3 more cars come in with the same issue.
Seems to only be affecting 87 octane so far. Not sure about 89. 91 and 93 should be ok. The direct injected engines are more finicky with fuel, but requires premium... and haven't had a problem with them so far.
*NW Indiana fuel from BP and Speedway have been doing the same thing* I don't know if Speedways in other states have contracts with BP.*
Shell, Conoco-Phillips should be ok.
If using BP, Clark, Speedway, Thorntons or any other brand that doesn't have it's own refinery, stick to premium for a month or so.