14 capital letters (Preview)

Hi Puzzlers! I got behind on my weekly posts here but I'm back now!

Let's take a look at this week's puzzle:

This week's challenge comes from Ed Pegg Jr. of Champaign, Ill. Take the phrase ZANY BOX KEPT HIM. Write it in capital letters. Something is special about the 14 letters in this sentence that sets them apart from all the other 12 letters of the alphabet. What is it?

Okay, this is different! I don't see much of a role for natural language processing here, but we'll try for a solution anyway.

The target letters (14):

•  ZANY BOX KEPT HIM
• A B E H I K M N O P T X Y Z (alphabetized)

The remaining letters (12):

• C D F G J L Q R S U V W

The fact that capital letters are used might suggest the solution has something to do with the actual shape of the capital letters--something that likely wouldn't hold true using the lowercase letters. Nothing pops out at me. We have various forms of symmetry and asymmetry in both groups. Open and closed forms in both groups. Varying numbers of pen strokes in both groups. Speaking of which...

The puzzle specifies that we should write the capital letters--I'm guessing it could be relevant that we actually write this by hand.

I just took a couple minutes to write it out by hand, multiple times. Also the remaining letters. Nothing is really occurring to me.

I also took a photo of my handwritten ZANY BOX KEPT HIM and tried rotating it, mirroring it, flipping it upside down, etc. Again, I don't see any pattern.

One big question here is this: Is the solution something inherent about the characters and their orthography, or are they related by some kind of real world knowledge? For the latter, for example, the 14 letters could represent all the digits used in Roman numerals (they don't). Or something along those lines, which would mean the 14 letters represent a real world closed class.

If we are interested in a closed class of some real world thing, and if the orthography is critical, then this real world class would have to be case sensitive, if you will. For example, US state postal abbreviations are always written in capital letters. Nothing comes to mind here. Letters from both groups appear in state abbreviations. 

Capitalization is crucial in the periodic table of elements, too, where both capital and lowercase letters appear. Maybe one of the two groups contains all the single letter abbreviations for elements. And... nope.

Okay, I'll have to mull this one over for a while.