iPhone deletes notes after editing or making a new note?

Hello everyone. I've googled this to death and cannot find even so much as a hint. My iPhone (iOS 6.0) today began doing the strangest thing regarding the Notes app. I'll attempt to explain it as best I can. I will add that my iPhone is set to not sync notes to iCloud.

I have dozens of notes in the Notes app. The phone is deleting any edited notes or new notes. If I am in Airplane Mode (with wi-fi + cellular off), all is kosher. If I edit an old note or create a new note while NOT in Airplane mode, the phone will delete the note as soon as I hit the "Notes" button in the top left hand corner that returns me to the list. I have rebooted the phone multiple times, closed all apps out of the multitasking bar, tried with connecting to wi-fi only, cell + wi-fi, cell only. Same issue. The new or edited note will remain in the list for a moment, and then with no observable event, just be gone. The list will update itself to go from 76 to 75, for example. I have free space on the phone, it is not full. It will allow me to store photos, videos, and create new alarms. The issue appears to be isolated to Notes.

I realize I could upgrade iOS, restore the phone, etc. but problems such as this should not arise out of nowhere, especially on something as stable as iOS. Can someone give me a clue as to what is happening, and how to resolve it? As you can guess by having dozens of notes on my phone, it's my main note taking apparatus. I'm fairly crippled without it.