The British to American English spelling dictionary "corrects" aesthetic to esthetic even though aesthetic is also used in the US. This should not be the case. The spelling "esthetic" on the other hand is used only in the US, though, so if the intention is for it to correct to "aesthetic" in British English, then this is an issue where this word has an additional spelling in American English and not British English, unlike the other words as far as I can see. Regardless, "aesthetic" should be allowed by the spell checker when writing in American English.

EDIT: From looking at the code, it appears like it only converts British English to American English, so I think these lines should just be removed. I am willing to open a PR to do so if the developers feel like this is an acceptable outcome.