It's not a bug! It's unintended irony!
Here's a really funny way to break Notepad that a coworker showed me this morning. I bet this is one of those jokes that's been around for ages, but this was the first I ever heard of it, so it's new to me.
This actually works. It will not crash your computer, it just breaks Notepad in that it causes it to display very oddly. No perm damage comes of the following steps.
Here's how to do it:
1. Open up Notepad (not Wordpad, not Word or any other word processor)
2. Type in this sentence exactly (without quotes): "this app can break"
3. Save the file to your hard drive.
4. Close Notepad
5. Open the saved file by double clicking it.
Instead of seeing your sentence, you should see a series of squares. For whatever reason, Notepad can't figure out what to do with that series of characters and breaks 
Again, it doesn't crash the app or anything, it's just a funny little twise of fate/unintended feature