Wheatfield Level Bug

I've just discovered a bug in the handling of Wheatfields, when you gain the ability to build higher level versions.

I have a small farming area set up like this:

.....W
..F.....F
W..W..W
..F.....F
....W

Obviously, these were all level 1 to begin with, then yesterday I reached a high enough level to build level 2 Wheatfields. The first change was thus:

.....1
..F.....F
1...1...2
..F.....F
....1

Shortly afterwards, I replaced two other fields as they expired:

.....1
..F.....F
1...2...2
..F.....F
....2

The thing that I've noticed, the two level 1 Wheatfields are no longer being harvested; 1 of them had 6 Wheat left to be harvested when I placed my first level 2 Wheatfield, but I have now had to replant that first level 2 Wheatfield whilst the level 1 Wheatfield still has 6 Wheat left to be harvested.

THank you , that must be why my lazy farmers earn nothing while they are surrounded by fields