Cannot watch local variable value if the function contains a "yield"

When I use the MonoDevelop to debug, the breakpoint set to a function which contains some “yield”, I cannot watch local variable value. It always shows “Unknown identifier”.
Is this an issue or need I do some settings for watching in this kind of function?

I reckon there might be cases where the debugger fails to address the local variables.
Your best call is to check the stack window in that case, or to actually create a swatch for your intended variable.

So put a breakpoint ‘before’ the routine call, and witness where it gets undefined, to understand if it’s a compiler problem, or a data problem!