We have a lot of examples of shifting stress when a word changes its relationship to what’s around it.

Try these two utterances:

I live in a white house.

He lives in the White House.

I don’t know if this effect is peculiar to English, but I do know that native speakers make these shifts all the time and without thinking about it. I never noticed it with those numbers before, though. To me it seems like the stress on the two syllables of “fourteenth” become more nearly equal rather than being distinctly on one or the other.

The difference is that Amendment starts with a vowel (A) which is a softer sound, so it makes the “th” in fourteenth more noticeable.

The word ‘fourteenth’ isn’t the issue – it’s the following word that gives rise to the issue.

The same thing would occur with any of the following:

Fourteenth undertaking

Fourteenth Ottoman regiment

Fourteenth International Conference (although the I is pretty hard here)

Fourteenth Elementary School

Fourteenth American Football Classic

I tend to think that the accent falls on the back syllable with the teens and the first syllable for numbers 20 & beyond. I think it helps alleviate mixups such as 15 for 50 or sixteen for 60. But the peculiar thing about this is that when counting we shift to the childhood habit of heavy emphasis on the first syllable for every number with the possible exception of 11 and the final syllable for those numbers above 20 except those ending in 7. Weird ain’t it?

I’ve honestly no idea what you mean. I don’t shift the stress anywhere.

Maybe it’s because I speak British English—also just known as English.

@Jeruba , Your white house example reminded me of how in Spanish the meaning of a phrase can be altered depending on whether an adjective goes before or after the noun. Link

I suppose it’s who you are and where you’re from
Like PO-lice and po-LICE.

I tried saying all the examples, and I didn’t notice any stress changing.

Did you say them at normal talking speed? I find it difficult to deviate from the rule I gave.

Yes I did.

Then you are a more agile speaker than I am. I am assuming that you always place the stress on the second syllable, since that is how the word is pronounced when it is not modifying anything.

Yes.