Oddities at the Post Office

This is weird. We're going out of town soon (that's not the weird part) and I wanted to put our mail on hold. I went to the post office's website, filled in all our info and under special instructions, typed, "Thanks!" But apparently, that's not a valid message:

Maybe, "Thanks!" is just too casual. So I upped it to "Thank you!" and tried again:

No dice. I figured it must have something to do with the number of characters used, so, undeterred, I gave this a shot:

And that worked.

That's weird, right?

It's probably weird that I'm thinking this much about it, but I can't figure out why you'd have to use a majority of the characters to make your message go through. Just add this to the list of things I don’t understand about the USPS. Like the number of signs in my local post office telling customers the post office trash cans are not for outside trash. 

This is a big problem? Really?

Oh well. I just hope the message gets through to our mailman. And I hope everyone who works at our post office knows I never bring in outside trash. Never.