The Great Button Mystery

If you've been following this blog (or know me personally), you know I like to solve puzzles. For example, how did the wallet of someone who lived a block away end up walled up inside my house? Well, I was recently involved in yet another mystery that has me completely baffled. It has nothing to do with our renovation, but I thought I'd share it here in case anyone had a theory that might explain what happened...

You may recall that my sister, Sonia, came to visit for the Inauguration back in January. While she was here, she lost a large button off her coat. We searched around the house for it, but it didn't turn up, so she figured it must have fallen off while she was out somewhere and it was lost for good. A few days after she left, Josh found the button in our car. I emailed her to let her know, and managed to hang on to it when we moved out of the house. A few days later, I stuck it in one of those little padded cardboard envelopes designed for mailing CDs/DVDs and took it to the post office to mail back to her. I even stood in line at the counter to make sure it had sufficient postage and everything.

On Tuesday, March 3, I had this email exchange with Sonia:

SONIA: I just received the button from my coat that you sent. However, I just received it AT WORK, and you clearly addressed it to my home. I am perplexed how it ended up in my work mail slot. I'm trying to figure out WHY it wasn't delivered to my home...it's not like it's too big for the mailbox or something. So weird.

NAINA: What's even stranger is that I mailed that button back to you nearly a month ago! WTF?

SONIA: Oh my god, so you did! Feb 6. WTF indeed!

So, can anyone explain why a button I mailed on Feb 6 to my sister's home address was delivered to her office (in a different city!) on March 3? Any and all theories are welcome, no matter how far-fetched.

[Oh, and if you don't know what WTF stands for, please don't ask -- you might be offended...]