Common Mistakes Writers Make #1: hopping through the tenses

I came across this mistake just today in a blog post I’d been reading—and decided it was an excellent opportunity to share this problem which inexperienced writers often have. The mistake? “Tense-hopping,” or moving from past- to present-tense (or any other tense) within the same fictional work. This error is easiest to fall into if one is attempting to write one’s novel in the notoriously difficult present tense, but it’s a mistake that can be made any time, really—and is worth learning more about.
 

The three most common verb tenses used by writers are past, present, and future; three less common are past perfect, present perfect, and future perfect. WikiAnswers says that there are also six progressive tenses, but I don’t particularly trust Wiki sites, and I think that if the progressive forms were important, I’d have learned them in my in-depth grammar curriculum throughout my homeschooling years. Disregarding those forms which I can’t define, let’s quickly look at what the six most common tenses look like:
 

Present tense: Hannah walks down the hall. (Hannah is walking down the hall at this moment.)
Past tense: Hannah walked down the hall. (Hannah walked down the hall a minute or an hour ago.)
Future tense: Hannah will walk down the hall. (Hannah will end up walking down the hall sometime.)
 

Present perfect tense: Hannah has walked down the hall. (Hannah is just finished walking down the hall.)
Past perfect tense: Hannah had walked down the hall. (Hannah walked down the hall a while ago.) 

Future perfect tense: Hannah will have walked down the hall. (Hannah is in the process of walking down the hall right now, and will have done so when she has come to the end of it.)Now, this is what it looks like when we “tense-hop.”

He watched her labor on. Only once during the race had she stopped—twenty yards before him, and she had shouted, “You are the most horrible brute in Owraith’s kingdom. Why do you not ascend to his throne? For you are worse than he! Kill me now, and have done with it!”

He stops to listen to her. “Eighth,” is all he says in reply. His hand went to his left hip, as though he would draw a sword. But for her to see that sword in the hands of a supposed madman would be his doom—psychologically and physically.
              —The Bridge Between Heaven and Hell (modified for these purposes), © Hannah Barta

Did you notice the mistakes? The final clause before the quotation in the second sentence reads, “She had shouted,” but the first sentence in the next paragraph says, “He stops to listen to her.” This problem lies outside grammatical rules and is, therefore, an aspect of your writing that should be eliminated.

Have you ever had this problem before? What do you think about it when you see it on blogs or in fiction?