Question - Histogram changes after export?

Question

When I export to a jpeg file from Lightroom, whether I choose sRGB or ProPhotoRGB, often but not always, the histogram changes dramatically.
In the worst cases, pictures that looked good and were well balanced are suddenly over-exposed with blown highlights (and I'm not talking fractions!)
Can anyone explain why this should happen and what is the best way of controlling results as I send the shots to magazines for publication?
p.s. I have just discovered that if I export to a Tiff file first, then export that Tiff to a jpeg, all in sRGB, it works and the histogram is barely altered. This has to be a bug, surely?

Answer 1

My comment was not directed at anyone particularly, but rather at Adobe.
I am tired and weary, after having paid thousands of pounds for their products to have absolutely no sensible recourse to help.
Their FAQ section is a joke and, like so many large companies that charge very high prices for their products, they abrogate responsibility and leave it to members of forums to provide the answers.
Indeed, it is something of a miracle to even arrive at anything approaching relevant in this area as their search engine seems to throw up just a very few and mostly obsure results when used. I entered 'altered histogram' and got a sum total of 14 hits, none of which were remotely appropriate. This, I have to say, is far from a new experience for me either, which begs me to ask just how unique is it to process RAW Sony files and convert to JPEG? That's all I do!
Certainly, I do admire those who are willing to offer their help freely. You, presumably, are one such individual.
Unfortunately, when all I want to do is work hard and earn a little money, to find software behaving inexplicably and then discover that I seem to be the only person in the whole wide world ever to have seen this effect, despite the millions of others doing pretty much exactly the same thing, I find it very hard to be bouyant and positive.
To get back to the issue at hand, I understand the basic mechanics of colour space (including the understandable but limiting fixation with ProphotoRGB in Lightroom).
It would, however, appear that I have now resolved the issue myself by reinstalling just about everything. Of course, I will likely never discover the cause, so pity the next individual who has been overcharged by Adobe and finds themselves in the same boat, when the only solution is a few hours of uninstalling, cleaning registries, reinstalling, etc.