Spell Check With "Muslim" & "Christian"

I was writing a Facebook status today when I noticed something.

Just so you know, Muslim is a noun. A man can be a Muslim, and that word should should be capitalized. But I had a moment's doubt as I wrote, because I was using Muslim as an adjective to describe a man and wasn't sure whether I should capitalize it. I began to type a sentence, "I just compared a muslim student to..." and this is what popped up.

Facebook informed me via spell check: It's not "muslim", my friend, it's "Muslim". Here's the corrected version.

Cool, I thought. Cool. But let me just see if spell check will be so punctilious about the word "Christian".

Nope.

 I haven't used Microsoft Word in many a long year, so I have no idea what Microsoft's spellchecker has to say on this topic. But I can tell you that Google's Blogger, upon which I am writing this, had the same objection Facebook did.

I might have more to say on this later, but for now, I merely point out to you that this is a thing.