Turn name bug?

[sedo]

I've recently started playing PON, and am having an odd problem where the month and year displayed in the top right seem to be incorrect. While each turn represents 15 days, the turn display advances a full month each time. After 12 turns, instead of starting with the next year (January 1851), the turns display as just the year (1850) without any month shown.

Judging by the arrival of snow is northern provinces, the game "knows" what time of year it should be using 15 day turns, but without the display it is hard to keep track. Oddly, this also happens when using the 15-day turn variant scenario for WIA (though the ones with one-month turns work fine).

I'm running the games on a Mac, using Wineskin, but they seem to work absolutely fine otherwise. Has anyone seen this problem before? Any idea what might be causing it?

-Sedo