I don’t know if this is because of any font issue, but to me the “boot” radical looks rather different than the component of the Kanji it is used in, such as 勤. In particular, in this form the radical is “missing” one horizontal stroke.
I find this a bit confusing because I can’t really see the boot (or the leather which is supposed to be part of “boot”) in that Kanji anymore (because it’s missing the “bull’s head” and I’m seeing flowers instead). Why wasn’t the radical chosen to look identical to its appearance in actual Kanji?
I think in this case, they used 堇 because it is that component, it just looks different when written in standalone form, (and it’s noticeable because that kanji on its own is rare if used at all in modern Japanese).
So they had a choice between using an existing character, 堇, that’s confusing because it doesn’t match exactly how it’s written in the radicals and doesn’t match exactly any kanji you’ll commonly encounter reading Japanese, or creating their own images to use in place of a character (which they do do for a handful of other radicals), and I guess in that case they went with the real standalone character. (maybe the wrong choice?)
Incidentally, an interesting tidbit - this seems to be one case where standard modern Japanese and modern Chinese style differs a bit (at least in how text is displayed online) - I can change the display of the character just by changing the display language:
勤 <- Chinese
勤 <- Japanese
勤 <- this probably defaults to Chinese unless you have your browser set to display things in Japanese.
Not sure at all if that’s because somewhere along the way a Chinese writing reform made the radical match the standalone kanji, or something else entirely, but it goes to show that it’s a writing variation that ultimately means completely the same thing - like g vs. ℊ
Hopefully once you know it’s a variation, the problem will dissipate naturally.
Same deal with the “Easy” radical back in level 8 - it’s taught as 易, but aside from the kanji that’s the same as it, every other usage of the radical has an extra stroke, a la 昜.
