One more jit.gl.pix question: unusual results from %?

I hope that I'm not being a nuisance or asking unnecessarily basic questions, but as I've continued troubleshooting ports from jit.gen to jit.gl.pix, I've noticed the following anomaly.

(cell.x + (cell.y * dim.x)) % 2

in jit.gen and the equivalent

((cell.x - 0.5) + ((cell.y - 0.5) * dim.x)) % 2

in jit.gl.pix often produce different outputs for the same input matrix, depending on the dimensions of that matrix.

The output of jit.gen is a series of alternating cells of 0 and 1 as expected, but some cells in the output of jit.gl.pix which should be 0 (i.e. multiples of 2) unexpectedly and seemingly impossibly have a value of 2.

If I take the jit.gl.pix cell index

cell.x - 0.5 + ((cell.y - 0.5) * dim.x)

modulo some other integer n and vary the dimensions of the input matrix, I can always find several states in which the index modulo n returns n instead of zero. Doing the calculation directly with the problem values rather than variables always returns the correct result, and the cell index itself is always calculated correctly.

I suppose that I could try to hack around this, but I'd very much prefer to understand whether it's a known issue, a bug, something I should understand better about jit.gl.pix, etc.

The included patch demonstrates this for a simple case (index of a 3 x 3 matrix % 2).