Well done on your success with English, given it's not your first language. Judging from your article you seem to have a better grasp of it than many native English speakers.
And yes, there, they're and their is one way to easily upset some of us. Not to mention to, too and two.
English, what a wonder it is.
Isn't it? But it's languages in general, I think. They grow organically and have a hard time fitting into rules.