Is celery-haystack not honoring prefetch settings?

[grayaii]

We've noticed that celery-haystack is sucking down all messages in the queue, despite explicitly setting these variables:
export CELERYD_PREFETCH_MULTIPLIER=1
export CELERY_ACKS_LATE=True
Using -Ofair while starting the workers...

We are using:
celery==3.1.25
celery-haystack==0.10
Django==1.8.4

I don't understand why this is specific to celery-haystack, but as far as I can tell, it is.