Baking – Why Does Glaze Soak into Doughnuts

The answer is simple: your test batches were less airy, and more dense. The heat from the oil was likely unable to penetrate the dough as effectively and cook the interior.

If the recipe turned out properly the first time around, that's probably not the issue. If your concern is with storing the doughnuts (though how you would have any left is a mystery to me!) then you may want to check out more effective methods of storage. There may be some helpful guidelines in this thread.

I'm a big doughnut fan. I've watched a lot of Unique Sweets episodes and it seems that the shops with the best doughnuts usually use a standard brioche recipe as it is rich in flavour, but also yeast risen... Thus it gives you the perfect texture and flacvour.

I wouldn't use ANY bread recipe that it measured in volume. Weight is far more accurate, especially for something with sensitive chemistry like bread.