If it makes you feel any better:
I visited in August, November and December 2001 and got normal visitor's stamps. The third time I came in I was asked why I was visiting the UK; I said it was my winter break, which was true. I was then asked what I did in the US. I said I was a musician, which was true. Then, where was I staying--I gave the same address I had printed on my landing card, which was true. Then he asked me "Who lives there?" And I told him, "A friend of mine, she's an opera singer." Which was true and perfectly legal as well since he did not ask me if she was my partner or my girlfriend! He let me go and did not take any notes.
I then entered as a student in March 2002. I applied for the student visa at the airport; however, you cannot do that anymore. I also applied under the private-tuition exemption for music students, which AFAIK has now been eliminated or at least tightened up to the point where almost no one can do as I did. So I was standing there at 7 in the morning, talking to this immigration officer, and I thought I was going to die. He asked me a load of questions, which I expected since this was a visa application rather than just a wave-thru on a visitor's stamp. But what really got to me was when he turned over my landing card and started making scads of notes.
Then he asked me about my job in the US. I told him I was on leave from an orchestra, which was true, but because I never had a contract from that orchestra I did not have to actually apply for leave, the whole thing was an informal arrangement. Other than that informal agreement I had been freelancing, working as an independent contractor, so the upshot was that I had absolutely NO WAY of proving that I had any work in the States. I was absolutely dying, worrying that he was going to call the orchestra (it being 2 in the morning where they were) and start asking them about this, and their story was not going to match mine. Let's just say that I did not tell any lies to get that visa, but if they had decided to really investigate, I doubt I would have been allowed into the country.
Finally he went off to see his supervisor for about five minutes. It seemed like forever before he came back with what I was sure was going to be a refusal form. But instead he said he was giving me a student stamp for one year, explained that I could travel as much as I wanted, stamped the passport, wrote stuff on the stamp with ballpoint pen, and sent me on my way.
I left and re-entered Britain about three times on that visa, and they didn't blink. The only thing they ever asked me was where I was studying. (Oh, and one person asked me what instrument I played.) I applied by mail for an extension in March 2003, and received my passport back within a week, with a new one-year stamp in it, no problems.
In October 2003 I went to the Consulate in New York and got an unmarried partner visa--no questions whatsoever about the student stamps. I don't know what the coding was on my first stamp, but it didn't seem to trigger any further investigation or suspicion.
