He'd forgotten all about the people in cloaks until he passed a group of them next to the baker's. He eyed them angrily as he passed. He didn't know why, but they made him uneasy. This bunch were whispering excitedly, too, and he couldn't see a single collecting tin. It was on his way back past them, clutching a large doughnut in a bag, that he caught a few words of what they were saying. (Harry Potter)
It seems ‘it’ and ‘that’ has no relationship of an expletive and its real subject. So the sentence looks clumsy to me. What do I have to consider not to?