No reasons for those to be confusing. However, unless you have a very advanced logical grammatical spell check, it won't catch a word that is spelled correctly, but used wrongly.
I HAVE gone back and read something I wrote and found that in my haste, I had used the wrong your, you're, their, there, or they're.
Most grammatical rules are actually sensible and logical. If you can diagram a sentence (a skill I suspect is no longer taught, except in college grammatical analysis classes), most spelling and grammar becomes a simple exercise.
And I've always said that was the one thing I missed about Bill Clinton. Even his extemporaneous expostulations were diagrammable.
Trucking to support the cats.