It might depend if the class is static or not. If possible please email the sketch to info [at] visualmicro.com so i can take a look.

Is the class in a library or a sketch code file?

The debugger has to inject serial code to work. It basically does what you would do yourself if you debugged an arduino sketch using the recommendation from arduino.cc to add serial.println() statements. 

The debugger adds/injects serial.println() statements with a known format so that VS can detect the serial output and "pretend" to be debugging.

This is not a perfect solution but works a lot better than users having to manually add serial.print statements to their code. 

If it can be made better that would be great, I might know more and be able to give better information after I see your sketch.

Sorry did you send your sketch?

As concerns the sketch stopping, you can only put breakpoints where a serial statement could possibly be put. This means that you can't put breakpoints in code that is initialized before the arduino core (and hardware serial classes) have been initialized. It's too early. This is the only cause of a crashing arduino that I have heard about so far.