Charles Schulz's simplified style confused some printers at first, leading to "corrections" that were more usually the opposite – erasing a character's eye after mistaking it for a misplaced ink blot, for example.
A strip of Prickly City had a glaring miscoloration that made the punchline hard to understand. The strip ended with Winslow being beat up between panels, but in the final panel, his color palette has been switched with that of Carmen. You can tell it's Winslow because he has a snout and tail.
This happens a lot in colorized strips. Full-color strips Monday-thru-Saturday are still a novelty that only some papers bother with, so for the most part these strips are produced only in black and white just as in the old days, and the colorization is farmed out by the syndicate. It's not publicly known to whom they farm it out, but there's strong support for the theory that English is not their native language. Exceptions mainly include big-name strips that are already produced by entire studios, and Non Sequitur, which is not colorized at all at the artist's insistence.
From about September 2000◊ to January 2001◊, the art on Garfield was very jagged and angular, particularly Garfield's face. This could've been due to a new inker or penciler taking over and not being as familiar with the "house" style.
Pearls Before Swine also parodied this once, in which the colorist deliberately colored the last panel wrong to be an ass to Stephen Pastis.
When Greg Howard handed off illustrating the American Sally Forth comic to Craig Macintosh (Howard kept writing for a while), readers protested that the new artist made the characters too thin. Macintosh began emulating the original style soon after.
Bill Mauldin once had Willie and Joe, the heroes of Up Front, being confronted by a superior while both were drunk. As Mauldin ruefully noted, some of his readers wondered whether he was drunk, too, as three characters had seven hands.
The 1970s The Broons and Oor Wullie strips were somewhat inconsistent when it came to the artwork, due to the new artist's rough style when compared to Dudley D Watkins. Hen Broon is probably the prime example - he can go from being slightly taller than his brother Joe to impossibly tall and skinny within a few panels. The artist also had difficulty capturing Oor Wullie's youth, sometimes making him look like a fully grown adult (albeit a short one). It was also not rare for characters to lose certain features such as noses or mouths.
The early Watkins strips from the 1930s are also incredibly inconsistent, although this can simply be put down to the legendary artist simply experimenting with new characters. The style didn't completely even out until around 1942.