Actually, on further inspection, I seem to be having a slightly different problem with the same error that I initially described now.

Even after modifying my code so that each python forked off to another process was only given the following arguments:
args = [(None, models_shape, False, None, [start, end], 'data/qp_red_features.npy') for start, end in jobs] 

where models_shape, start, and end are only single integers, the same error still comes up as a result. Within each process, I'm reading in a (relatively small, only 12MB) .npy ndarray and taking the [start:end] slice.