When you start learning a language and think you’re starting to get the hang of it, you might think you spot errors.
Now, some of those might be real errors, but some are merely you overgeneralising or misunderstanding.
Two examples of my own: when I started learning Greek, I thought that αεροπλάνο was misspelled because my dictionary gave αήρ for “air”—surely, there should be an eta instead of an epsilon in “aeroplane”, then!
Then, later, I learned that the stem of “air” is αερ- (see, for example, the genitive αέρος); I had been misled by assuming that the nominative form (the citation form, found in dictionaries) is the stem or basic form used to derive words.
Another, much more recent example: I had assumed that places that gave kammit as the Inuktitut name for a kind of boot used by Inuit was a typo for kamiit: someone doubling the wrong letter when typing.
While that’s plausible enough, I later learned that inflection used to be more complex, and that the “add -it” rule for forming plurals was a simplification/regularisation/analogical change that is comparatively recent. And it seems that kammit is the older, conservative plural, which is still in use by some people, and kamiit is the newer, more regular but innovative form.
Moral of the story: some errors are real errors, and some are just you not knowing all the rules :)