The more things change, the more they change

I saw a headline in the Salt Lake Tribune the other day which informed me that the police had caught a number of thiefs. My spell check is objecting to that word even as I type. So, what is going on? Is it a simple matter of a writer/editor who can't spell?
No, there's more to it than that. The traditional spelling of the plural is, of course, 'Thieves.'  It falls into a group of words who change one of the sounds as it becomes a plural: sheaf/ sheaves; leaf/leaves. This is in turn a carryover from the time when English was still true to its Germanic roots. In a number of Germanic languages, a sound may have two versions, one voiced and one unvoiced, depending on where it is in the word. Our f/v combination was once that way. That is, the sound written as "f" would be pronounced "f" in some settings, and "v" in others.  In some cases, the sound distinction is noted, as with f and v, but in others, it may remain spelled f, yet pronounced v in certain cases.
As language changes, and plurals change (the plural of shoe was once shoon), the distinctions in pronunciation and articulation become distorted or even disappear. So, someday, the plural of thief will actually be thiefs, and the writer will be simply ahead of his or her time.