Either I'm missing something beyond obvious here, or something has gone seriously wrong with my development environment under the debugger.
Here's the first call, with the value for the parameter shown:
And then, when stepping into the method, the next line on the call stack, I am seeing:
I have cleaned the solution, rebuilt everything with no errors, restarted Visual Studio, rebooted, and it is still acting like this.
What is going on here?