There are known problems in Visual Studio 2008 SP1 related to breakpoints and debugging experience with multithreaded applications. Since these days almost everything that you write is multithreaded app, I would recommend you to install the hotfix from MSDN Code Gallery.
Here are the possible symptoms:
- Breakpoints in parallelized loops are eventually ignored after multiple hits
- Stopping and starting threads causes breakpoints to be missed
- Visual Studio may crash when you debug multiple processes at the same time
- Stepping over a disabled breakpoint when you debug a native application turns into a “go”
- Stepping when you debug a managed multithreaded application can randomly turn into a “go”
- Visual Studio crashes when you use the “Step Into” command to start an MPI program
- Running the “Step Over” command while you are debugging multiple processes causes a deadlock
- Disabled breakpoints are not visible after you install Visual Studio 2008 Service Pack 1