I had an English teacher in high school who was highly attentive to this sort of construct. He would return many a paper with "VPR" marks sprinkled throughout for 'vague pronoun reference' and points deducted accordingly. Certainly a common error.
After a few minutes of talking to him it's very hard to figure out what he's saying because he'll have dropped nouns all together in favor of pronouns. This can get very confusing when talking about technical stuffs.