UPDATE:
It seems to happen on the snowy kingdom preset too, with desert villages, shipwrecks and other structures spawning. I am yet to see if it happens on any other presets but that is what I have found so far.

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I remember 3, 4 years ago I'd always go on the Desert superflat preset on minecraft because it was super glitchy, mineshafts would spawn everywhere, etc., it would be pretty fun to build there and everything, so I decided to go back now and see what's changed, if it's still glitchy and it seems to be that a new glitch in this preset has appeared in 18w11a...

Everything seems normal, until you see shipwreck structures, jungle temples, witch huts and other structures generating in the so called 'desert', where only desert temples and villages should generate, as I believe.

I can take more photos of the actual structures up close, like the temples, witch huts, shipwrecks, etc. It actually seems kind of cool, although if you want it to look like a legit desert how I assume, you probably wouldn't want JUNGLE temples and witch huts in it.