I suspect someone set the growth_period of wheat very low for testing purposes and forgot to assign a final time for release.
Currently, the growth_period is set to 3h. By comparison:
The problem with such a low growth_period is that even a single 11x11 patch will produce wheat so quickly that a pair of farmers will have barely finished harvesting the crop and planting a new set of wheat before it is time to harvest it again! It’s pretty much impossible to grow anything else when you’re growing a moderate bit of wheat.
I suggest the growth_period for wheat be set to somewhere in the 9h-12h range. Wheat takes longer to grow than any of the other crops in reality, but growth_period is balanced ingame by the value of the crop. You might want to adjust the amount of wheat it takes to make flour to compensate for the slower growth cycle.