Odd characters in debug terminal

I'm seeing some odd behavior in my Crossworks for ARM project. I'm running on an STM32F405 and when I'm debugging, I get characters appearing in the debug terminal and then being deleted quickly. A lot of times, it's a "p", but not always. It's not expressly being generated by my code as far as I can tell. There are only a few debug_printf calls, but they're not being called. I put a breakpoint on debug_printf and it never triggers. I did a little research on Cross Studio IO and ITM, and put a data breakpoint on writes to 0xE0000000 and that never triggers either.

Here's a screen capture of what happens:

http://www.rjmmusic.com/DebugTerm.mov

I assume that something in my code is doing something it's not supposed to, but I can't figure out a way to catch it in the act. Anyone have any suggestions on what I could try?