Broadly: How sad.

Musically: I caught the change and definitely thought it was unusual. It brought a mildly aggressive feel to the later section of the song.

If I’m remembering right it opens in Dm and then goes down to F#m after the first chorus. So pitch wise a shift downward, but maybe you’re talking counter clockwise on the circle of fifths or something?

Edit: when I first commented I either didn’t see the Strawberry Fields reference or it wasn’t there yet. We’re probably not talking about the same thing, but definitely give the acoustic version of Pool Shark a listen.

Your Strawberry Fields reference made me curious though and I found this interesting snippet https://www.reddit.com/r/beatles/comments/5fgser/the_famous_splice_edit_in_strawberry_fields/

Oh man, I figured a question like that would follow. Now I gotta listen to polka to remember what the songs were like. 😅

So, I only know the German titles, and these are like the low-hanging fruit, the pop songs of the polka genre. I’m sure, some polka connoisseurs would have wildly different suggestions.

Kind of the most stereotypical always-getting-played polka is “Böhmischer Traum”. It largely follows the structure I wrote out up there, although it actually puts a load of complexity on top.

Then the polka that always got the most excitement out of the crowd when we played it, is “Die Sonne geht auf”.
It’s a relatively non-standard polka, though, with relatively much influence from marching music, and somewhat more concert style, i.e. not really something you’d dance to.

Well, and for a polka that really follows that structure almost to a tee (with e-flat instead of d-flat), there’s the “Kuschel-Polka”.

Some others we frequently played: Morgenblüten, Slavonicka-Polka, Wir Musikanten, Böhmische Liebe, Südböhmische Polka
I’ll leave it as an exercise for the reader to find out, if these ones actually match the structure above. 🙃

Edit: Oh, I forgot another pretty much always-getting-played polka: “Auf der Vogelwiese”