> the USSR was exporting plenty of 'collected' food to Europe while the Ukranians starved

The USSR exported some food because the government had underestimated the extent of crop failure, but the food exports themselves were severely cut back upon as it was realized that the crop was not what had been forecast. The grain exports in themselves were nowhere near large enough to account for the famine as it actually did occur. That was a consequence of the fact that real crop failure was not well enough appreciated in time.

There was a whole body of literature produced during the Cold War which aimed at hyping the story of food being shipped away as the cause of famine. Mark Tauger has an interesting piece on his site which documents the administration of food aid in the Ukraine during 1928-9. It also appears in Donald Raleigh, (ed.), PROVINCIAL LANDSCAPES, under the title "Grain Crisis or Famine?" One should be rather wary of stories produced in the Cold War environment.

As already noted, the root cause of the stories taking off the way they did was the fact that the rustic plant diseases which Tauger discusses could reduce the crop while still allowing the grain stalk to grow. This fed the story of a big crop from which the grains were apparently missing. No one figured it out in time.