Bug/Issue Singleplayer price hikes at Carpenter and Blacksmith

I received the letter Spring 1 year 2 saying prices were going up. I'm in singleplayer, with no cabins on my farm. Now I'm supposed to pay 250g for one lump of coal, when the sell-to-Clint price is still the same?
Are you quite sure you didn't forget to put an if block around the code, something like:

if Game1.isMultiplayer
{
//Jack up prices to counter the effect of up to 4 people making income
}
else
{
//Give single players the same ridiculously expensive prices
//they've been paying since the game was released
}