grammar - Have had or Have been

I've been learning English in my company.
We have just started Present Perfect and encountered 1 issue I don't quite understand.

There were 2 different, not related to each other exercises.
In one we had to rephrase the following sentence using Present Perfect:

1) I got this job in January.

In the 2nd excercise we had a list of events. The last two are:

2001 - moved back to the USA and went to work at the M&M factory in Montana.

2006 - moved to A new job in the M&M offices in Nebraska.

Using this information we had to make a sentence in Present Perfect out of words

2) have/job/Nebraska

and since/for/from...to. Since the prompts clearly point out to the last of entries and we have no info on what happened to "him" further, I supposed that only 'since' could have been used here.

Most of us gave the following answers:

1) I have had this job since January.

and

2) He has had a job in Nebraska since 2006

Our teacher said that considering information given in tasks, the 2) answer is correct, but the 1) answer isn't. The proper answer to the 1) is:

1) I have been in this job since January.

To me they have the same meaning and both are suitable. Both cases seems to be related, so I asked what's the difference between 2 answers and why it's wrong to say "I have had" in 1) as we did in 2) example. He said the reason lies in the fact that in 1st case there is "this", more specific, and in 2nd case we have "a", which indicates something general. Therefore, there is no way we can use "have had" in 1)

The lesson ended and he told us to investigate this as our homework. I've spent a great deal of time considering this and searching through the web, but still have had no answer.

He is a native speaker, British, wearing a bow-tie, speaking with that funny British accent, scrupulous and addicted to proper grammar. It's rather odd not to believe him.

But it still bothers me, is he right? Does the presence of this/a has so much impact on usage of have had?

Answer

I am also British, and I say there is no semantic difference between your answer for question 1 and your teacher's answer. Also, they both have valid grammar and as such they are both correct.

It's possible that in your teacher's variety of English his form is grammatically preferred over yours, but without a wider context to the phase it's hard to say.

The presence of the near demonstrative "this" gives the sense that the speaker is saying it while being in the workplace, perhaps while actually working. In that case, in British English, it sounds a little more awkward (though not incorrect) to use "have had this job". The most usual form in that situation would be "have been working here", but that's further from the original form of question 1, so maybe that's why you're teacher went with "have been in this job"

But really this is splitting hairs and your teacher shouldn't have marked you incorrect for "have had this job"