debugger halt after start(), can only resume in update

When I tried to use monodevelop as debugger to debug my start() function call for an object, the debugger halts after start() being executed. There is no immdiate, no call stack, no thread or anything down in the resource inspector. the debugger still respond to my input and breakpoints but I can't use step in, step over or even continue, it just halts, and the unity editor is obviously freezing in the debugging mode. Only if I set a breakpoint in update() function for that object, the debugger resumes. But I need to see the variable changed during start() and update() due to a bug that appears no where. I can't do that because mono won't let me, it halts after start().

Why does it behave like this? Is this a BUG?